If the game gives a current experience value then you can search for that. If you can gain experience then fight, try not to use items, do a scan afterwards to see what increased.
That said assuming you are after the SNES version then someone has already figured out things for youhttp://datacrystal.romhacking.net/wiki/Breath_of_Fire_II:RAM_map
The pointer may not be in RAM and may instead be in the ROM somewhere, or read from the ROM. That said as you know the RAM address you would probably tell a debugging emulator to do a break on read and break on write to the experience location. That might not immediately give you it but it will give you the instructions leading up to it and you can go back, trace if you will, up through the code.
Assuming you are indeed using the SNES version though it seems some of the work has already been donehttp://datacrystal.romhacking.net/wiki/Breath_of_Fire_II:ROM_map
Were I to hack it on a modern system I would probably do something with a slide code, though with a bit of asm you can probably make it add to each character. Though at the same time if it does do only in active party then 7E:5050 - 7E:5053 and 7E:5054 - 7E:5057 detailing your party might be involved as a middleman.
With that said if a misgiving you have is a forced character then "7E:51E4 Bit setting for PC availability or Valerie." might be of interest.