Fun fact. This original song, Cerebral Cobweb, was made by Fleetwire. I'm not going into detail about what he did, but that's beside the point. Fleetwire also made the music for one of Krinkels', the creator of Madness Combat, spinoff videos titled Romp.fla. Basically, Cerebral Cobweb is from Madness Combat, not Geometry Dash. Still a great edit.
Mostly by ear/musical training here c - g# - g - g# (one octave lower) - g - f (octave up) g - f - g (octave down) those r the first few notes u can probs figure the rest out