Many cuts are commonly employed for pork schnitzel, but some options are better than others. For a classic pork schnitzel, the best candidate is a boneless loin chop.
Although on the leaner side, a loin chop is one of the most flavorful pork cuts due to its sourcing from the top loin, and it's texturally consistent, making it cook evenly.
A small external layer of fat keeps the pork moist, even when pounded flat. Once breaded and fried, the loin chop produces a perfect pork schnitzel, a cut above the rest.
If you're making a Vienna-style schnitzel, you'll also want to generate an airy bubble between the breading and the meat. This is easy to do with a boneless loin.