I need to find an equivalent transistor to a SE110N. I'm in downtown, stores are opened, they'll close soon, so if I could solve this now in the next minutes, I'd greatly appreciate the help. Thanks in advance.

 

Not sure, but seems to be a voltage detector/MOSFET of some sort, rated to detect 110V and rated at 20ma.
I've seen one cross reference to a NTE7215, called an Error Amplifier/Voltage Detector.
Good luck.

https://vetco.net/products/nte7215-ic-error-amplifier-110v
That links lists this as a replacement for the SE110N (near bottom of page)