That dome shaped chrome cap probably unscrews with a wrench, or a strap wrench.
The chrome barrel behind it might just pull straight off, or might also unscrew, probably just slips off.
Then you can take the cartridge inside there to a plumbing supply shop to identify and replace.
The whiter piece with the screw looks to be some kind of stem extension or handle adapter, not part of the cartridge, so you will need to keep that part to re-use.