This one was produced by Zico.

I actually prefer Bebop https://youtu.be/Gos45jVkRCY
The one the yellow t-shirt is Dongsoo and the one in the red and black long sleeve tee is Namhyung.

There are so many trainees who’ve already debuted before – Nu’est is just the more well known group.

Ju Wontaek and Kim Yongjin were both part of Underdog (although not at the same time I think).
Taehyun and Sungwoon are part of HOTSHOT.
Both Kim Dohyun and Park Heeseok are from X10.
Both Jung Woncheol (the guy who did N’s dance in the intro vids) and Insoo were from A6P. Insoo also participated in Boys24, as did Kim Taedong.
A-tom/Kim Sangkyun is a part of Topp Dogg. He was also on SMTM4.
Cho Gyumin (IMX ent) was part of Alpha:Bat Duo.
The IT entertainment Boys Han Minho and Lee Seokyu were part of Pure Boy.
Kim Chanyul and Choi Hadon are part of JJCC.
Kim Jaehan (MMO) was part of OneVoices before they disbanded.
Kim Taewoo is a part of Rion Five.
Son Dongmyeong (RBW) is part of M.A.S 0094
Choi Junhyung is part of indie idol group AFOS
Yoo Kyungmok was part of BTL before they disbanded.

This is a great and reliable resource for any idol group info you might want. They don’t post information unless it has been confirmed https://kpopinfo114.wordpress.com/2017/03/16/produce-101-season-2-contestants/

Wang Minhyuk was a member of NPI (New Planet Icons)
Kim Seongri was a part of K-BOYS
Oh, and Lee Gwanhyun also participated on BOYS24.