Can you play Nocturne from Traveling Merchant discard effect?

No. Nocturne's ability only triggers when you look at or reveal him from the top of your deck. Discarding (hand to trash) and drawing (deck to hand) are not looking at or revealing — they don't trigger Nocturne at all.

Traveling Merchant says "discard 1, then draw 1." Neither step looks at or reveals cards from the top of your deck in a way Nocturne can respond to. Drawing is a completely separate game action from "looking at" (FAQ #3447, FAQ #1433).