Okay during this part - When everyone's attention is on Tae holding the book with the drawing, Jin is thumbing through stuff on the desk - JK's attention is on what Jin is doing, when he finally looks over to see what Tae is holding, he grabs Jin by the waist, pulls him along and then squeezes. (video below pics)

VIDEO - HERE  See footnotes for 'waist/hip touching'.

THE ARMS - Jungkook just HAS to touch Jin. Jin's accepting body movements - he doesn't object..in fact, I think he is quite used to this.  Video - Here

JK likes to play with Jin's arms, likes to touch his shoulders, etc...on average, a lot more than he does with any other member.

PERSONAL SPACE - All of Bangtan stand close at some point, some more than others, but 98% of the time - Jinkook are always this close (check any video ever captured where they stand next to each other) - 9 times out of 10 you are going to see Jinkook standing this close (and closer) even at times when no one else does.

In their own world - Jinkook like to bicker..and play..and touch...and talk..sometimes like they are the only two people in the room. You would never guess there is an between them - and sometimes you ask yourself - who is the youngest? oldest?  See this video for reference, lol and eye contact even when they aren't next to each other, here. Also just talking here, together in their own world.

When everyone else's attention has moved to Jimin - Jinkook are still in their own world

VIDEO - HERE

MIMICKING/MIRRORING  - intentional and subconsciously. These two have taken on each other's nonverbal actions. definition of mirroring is in footnotes (it's important to understand)

Their mouths - VIDEO Slightly off in timing - but mirroring none the less.

Also (from another video recently) lip biting at same time. Lip biting is one of JK's biggest habits - you can see him doing this a lot in their vids- recently, I have noticed Jin doing this.

Intentional (from another occassion)- In vids I have seen of this moment, Jin does the finger to cheek gesture first, then JK copies him:

Amused and laughing at each other's antics - Jinkook love to make each other laugh, but not only that - Jinkook laugh a lot at each other when the other does something that the rest of the members might not find as funny (with exception of Jimin who laughs at everything hehe)- you can always see JK and JIN cracking up at something the other did.

Also - they tend to look at each other for validation - are my jokes funny? JK thinks so (or Jin thinks so). Then they are happy happy.

UPDATE: (I wanted to watch the behind the scenes to be sure before I posted this part)

During Jin's Interrogation scenes, JK can be seen doing some interesting things (since it was pretty clear he wasn't a part of the scene during the whole part of the skit) - but he was hanging out and roaming around during most of this..and thus..the pushups? Why now? Not once, but twice (in the behind scenes and v live skit)

I'm pretty sure Jin noticed at this point of talking to Jimin too - several times Jin's head was facing towards JK's direction and not up at Jimin)

This set of push-ups in the behind-the-scenes is different from the one in the V-Live. Jk is well into doing these - he gets tired, stops for a second and says, "Wow, this is tiring." Now, listen in the background - whose voice do you hear? Jin's!  Watch Jk's eyes turn towards the direction where Jin walks in shortly after and you can see a sudden expression of seriousness, he goes back to his pushups with a sorta renewed sense of vigor (not to mention he was asked, "what are you doing? are you the superintendent?" He answered no..so was he even supposed to be here for this scene?)..now after Jin finally walks by, JK stops. Video HERE (I edited out the up/down of his pushups to make gif shorter.)

I left this image full size so u can see the difference in expressions from before to after hearing Jin's voice)

The stare - lemme just put it to you this way - the video was a lot of Jk staring..but the b-t-s video wasn't cut from 3:51 to 4:04 and JK was intently staring at Jin the whole time. (at 4:00 they both did a small giggle hehe)

During the name game - Jk just stood there, watching both Namjoon and Jin do their little battle. JK's stance - HE KEEPS HIS HANDS IN HIS POCKETS - this is a common verbal sign of a man wanting someone to notice his...crotch. (but, I won't get into that because it might not mean that for him...but lets just say he did it the whole time he was around Jin *wink*)

Now mind you, JEON JUNGKOOK is not Detective Kim - but ...well...whatever... lol (any oppurtunity to touch Jin, why not?!)

BONUS: 

JIN is 'O' bloodtype and Jungkook is 'A' - Blood type's best suited to each other:

The best partner for a Type A is a Type AB or a Type O– their reliability will put the A Type at ease and offer them some of the security and stability they crave. 

O Types are easy going enough to make a relationship work with most blood types. However, they’re best suited to Type A. Both Type O and Type A blood types have a vigorous work ethic and O Types are typically willing to take the reins of the partner, which takes some of the stress off the notoriously tense A type.  source

This is just from today's video - there are tons and tons of references and stuff to psychoanalyze when it comes to Jinkook.

FOOTNOTE:

Mirroring is the behavior in which one person subconsciously imitates the gestures, speech pattern, or attitude of another. Mirroring often occurs in social situations, particularly in the company of close friends or family. When people are interested in one another, researchers have found that they tend to mimic each other’s movements and gestures. Two people who are attracted to one another end up in synch with one another. They pick up on one another’s mannerisms – perhaps adopting similar speech patterns or turns of phrasing or performing similar activities like taking a drink at the same time.

Waist/Hip touching in couples:

 If he touches your Waist - OK, this is probably one of the clearest. He. Is. Into. You. It’s probably a signal for other guys to back off because you are already his. Or you’re probably already a couple and he wants you to be by his side. Congratulations. source

When a guy touches your waist/hips, it can mean several things. It can be a protective gesture, a gesture of desire, and/or a gesture of affection. It's an intimate thing to do, and inappropriate unless you're flirting or dating.

TOUCHIN IN GENERAL : A man who is interested will find any excuse to touch you. This could be anything from simply touching your arm when you say something funny to reaching over and brushing an eyelash off your face.

LAUGHING: Does he laugh easily around you? A man who is attracted to and comfortable around you will laugh more easily than a man who couldn't care less. In addition, he may try harder to make you laugh or get you to notice him. If your date is exceptionally silly around you or exceptionally loud when you're in the same room, you can bet he's hoping you find him as funny as he finds you.