There's a long list. The one that comes to mind chronologically early is securities fraud in accumulating shares of Twitter. Though it's probably past being prosecutable, visa fraud in immigration status. There are dozens of crimes in DOGE.
Congress has the power of the purse. Congress has decided to allocate some money to USAID. Enron Musk came in, and redirected that money. Thats illegal.
On the one hand, he said he'd go to jail if the dems won. On the other, he says a lot of things that aren't true.
At this point, Musk might face extradition claims outside the US and state-level charges within it, even if Trump pardons him for all US federal laws. And he might have lost a lot of leverage with the US federal government by having SpaceX stop taking customers for more Falcon launches before Starship's fully ready.