There is no prescribed dress code for AIIMS entrance exam but it is advisable to students that they don't wear any eye catching cloth in order to avoid any hassle at the exam centre. You can wear full sleeves shirts or t-shirts but make sure they don't have big buttons or any vague writing on it. Don't wear hat, cap and fancy googles. 

You can check exam day advises on careers360 portal

https://www.google.com/amp/s/news.careers360.com/aiims-new-delhi-releases-aiims-mbbs-2019-exam-day-advisory/amp

Hello Ravindra,

Full sleeved shirts or t-shirts are not allowed in AIIMS 2019 examination. Half sleeved shirts or t-shirts with trousers are allowed. Keep it simple and easy. Also, avoid the list of prohibited items by AIIMS like jackets, headgears, wrist bands, rings, goggles, etc.

Thanks, hope this helps.