Every program uses its own port, so it depends. You CAN find out what port a program is using right now, but depending on program it might use a different port next time you open it. Some programs allow you to fix the port so it always uses the same, and many just have default ports defined you can change.
OP talks about allowing incoming connections, so he's asking about a listening port
if listening port changes every time the wallet opened, how would others know it and connect
I have an internal IPv4 NAT'ed lan, but often have wallet syncing problems... Now you can "allow incoming connections" that you can tick in the options but nowhere is there talk about WHAT port... Undecided
I think "allowing incoming connections" won't help your syncing problems
it enables other peers to connect and download block from you, sync from you if they have lower block heights
what kind of syncing problems you have? slow/throttled or totally not syncing?
Or any way to find out what port it uses?
here's one I know you can do from your gui wallet,
on your wallet's console, typing
getpeerinfo will return a list of peers connected
on one of the peers, look for something like this "addr": "37.120.190.76:8555"
that's the IP of other peer and 8555 is the listening port (default for BTX)
on your side by default your wallet will use the same listening port number, if you choose to enable it