I am not sure this is the right question to ask! How far behind is Chinese domestic engine compared to GE or Rolls-Royce?
Can China export J-10C or J-31 with domestic engine WS-10A. By the look of J-10C, it's a good bird except Russian engine.
US beat China to figuring out problems with a 195kN engine in their F135, but the WS-15 will also be 3D TVC so that’s an additional challenge not faced by F135.
Russia is also making a 3D TVC engine in the same power class. It’s not known whether they are closer or farther away than China on finishing it.
The J31 cannot fit a WS-10 engine, they are too big. Besides, J31 is not a finished plane, just a contender to the J-XX program. It can however accept the WS-13 engine designed for drones and JF-17 which was the planned power plant.
Only the later J10 variants use WS-10 variant engines. Afaik the standard export J10 variant (based on J10A) uses a Russian engine to cut cost and protect domestic technology. That said, if someone with close relations like Pakistan asked for the most powerful J10, they could probably get it, but it would cost them.
Right now there’s not a lot of demand for high end fighters. The large budget countries are either hostile (US, UK, Japan) to China or allied but fully able to supply themselves (Russia). Saudi Arabia is a prospect, being both rich, kind of non aligned and non self sufficient, but they’re on paper an US ally, so export technology could face restrictions.