If you could provide an example (YouTube video, Soundcloud track, etc) that would help.
There are a few potential answerrs to your question.
1. The Chorus effect actually kinda does that. It copies your signal and slightly detunes it, giving the effect of 2 guitars. YMMV.
2. Smart Harmonizer on your POD. Plays the harmony part for you. Pretty common sound. Just don't play the wrong note.
3. Dual output guitars going through 2 signal chains.