Assalaamu alaykum. Is it ok to pray with a watch on your left wrist as you cannot grab the wrist as well? Also, several hundred fish oil capsules contain the same amount of alcohol as a light beer, so one capsule contains the same as a glass of orange juice. Are fish oil pills halal?

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger. 

First of all, you should know that placing the right hand over the left hand in prayer is a Sunnah and is not obligatory. If the worshiper does not do so, his prayer is still valid.

Also, wearing a watch on the left wrist does not prevent placing the right hand over the left one; this is nothing but an illusion from you. Therefore, the prayer while wearing a watch on the left wrist is valid and there is nothing wrong with it at all.

As regards your second question, please refer to fatwa 299059.

Allaah knows best.