Answer: Go to Gmail and send an email to the other party "can you Skype now?".
Literally. I had to schedule a video call recently by email. There is simply no formulation to schedule a video call using the name of one of google's products.
"Can you Hangout tomorrow?", "Can you Duo tomorrow", "Can you chat with Allo tomorrow?".
Nothing would work without confusing the other party with some probability. "Can you Skype tomorrow" always works, with everyone, no confusion.