if i have a cost reduction of 1 for spells. and i play a 2 cost spells with a 2 cost repeat. what does it cost?

3 Energy if you pay the Repeat (2 base + 2 Repeat − 1 discount). If you skip Repeat, it costs 1.

Repeat is an optional additional cost added to the base cost, and a generic "spells you play cost 1 less" discount applies once to the total (Rule 356.4, 820.1). The discount never applies twice — one discount, one spell (FAQ #9223).