Korean Mun, but which one?

Obverse: Sang P'young T'ong Bo

Reverse: ?

I don't think your particular type is listed in the Numista catalogue at the moment; better pictures of the reverse might help to confirm or deny this.

For reference, this is what I see on the back:
top: 訓
left: 五
bottom: 二*

*possibly 平 or 干. I'm not 100% sure about the one on the left either, only absolutely certain about the top one.

Similar coins:
https://en.numista.com/catalogue/index.php?mode=simplifie&p=1&l=&r=%E8%A8%93&e=&d=&ca=3&no=&i=&v=&m=&a=&t=&dg=&w=&u=&f=&g=&c=&tb=y&tc=y&tn=y&tp=y&tt=y&te=y&cat=y

I can confirm this coin is not on the Numista site, I've only found similar ones in Krause. Additionally, the only way to get better reverse pictures would be to start with a better coin.

The reverse bottom appears to be 中 to me.