How much of your profits go toward taxes?

How much of your profits go toward taxes?

I just started trading and learning from my friend.

Last year he made $800k off option trading and has an annual salary of $200k in NJ.

How much of it does he actually get to take home? Would he be paying the taxes when he files for the year? Really curious but don’t want to ask him directly.

Also if my account is down for the year do I have to list on my returns?