As you can see from the above picture, Yoona thanks 5 SJ members in SNSD Oh! album.
The 5 members are Eunhyuk,ShinDong,Eeteuk,Ryeowook, Kyuhyun and also TRAX member, Jungmo.

This is what the highlighted parts says.

Thankful to Hyukjae oppa & Shindong oppa. We'll do an encore concert ㅋㅋ troublemaker and close oppa Court Lady* Teuk and my three oppadeul Gamekyu, Seowook, Jungmo.

* Reference to him being the Milk Club president

Milk club is a club that Eeteuk created and he is the president of it. :)
If you do remember, Eeteuk always mention about the club in his cyworld last time.
Of course, Yoona is in that club.

Credits: Sj-WORLD
reported by ting18 @ DKP