It's held by Christopher Wray, who is serving the 10-year term prescribed by Congress in an attempt to distance the FBI from presidential politics. Trump himself appointed Wray in 2017 during his previous administration, but then soured on him after he testified truthfully to Congress that there was no credible evidence that Joe Biden won the 2020 election through fraud.
So the first question is whether Trump can throw out Wray (like his predecessor Comey, a lifelong Republican) on a whim. The second question is whether the U.S. Senate will confirm as FBI director the cretinous Kash Patel, whose only visible qualification seems to be an unbounded eagerness to unleash the power of law enforcement against Trump's enemies, public and private.