"If he trade under S corp and LLC and show some other expenses so K-1 will have less profit or a loss. Please advise"

I would advise that you are both a bit out of your field of knowledge.

"If he gets a profit, he will adjust with expenses like Rent, office supplies, office expenses"

Nope. That is not how any of this works. You don't get to "adjust". You Report what is incurred.

"If he gets a loss he can show that is K-1 ( in personal tax there is a limit of $3000 loss per year)."

Now you seem to be confusing income and capital gains.

I would start here:

https://www.irs.gov/taxtopics/tc429