Scratched Transistor
The manufacturer has scratched off the identification to make it so that it's not easy to copy or repair his product.
This means you'll have to take the less easy route.

Trace out the circuit - looks like a 2 layer board so should be straightforward
Run the circuit while measuring various parameters, with a DMM at least, and preferably with an oscilloscope
Figure out from the circuit and measurements what parameters the transistor needs to have
Select any transistor with at least that performance

There may be a simpler solution, and that's to search the heck out of any identification you have on the product, or the board (I can see a serial number or something peeping out from underneath the transistor). You never know, somebody might have already reverse engineered it and published details.