My friends brother got arrested for carrying a illegal weapon and he was a felon. He received a slap on the risk and probation. Recently, he was just arrested on a felony gun possession charge again. This is his first probation violation but what should she expect?

Jail time.
Clearly he hasn't learnt anything,.

How and why he only got probation is beyond me? Good attorney? Bribe to the judge? Almost all gun possession charges by a felon end up with a 5 to 10 year sentence with at least 1/2 served.

So what was the probation time? 5 years probation? He can look at serving that. He should have a very very good attorney.

... Recently, he was just arrested on a felony gun possession charge again. ...

Both previous answers would depend, of course, on whether the court finds that he is guilty, again. In other words, arrest and guilt are not the same thing.