What parts of a spell does the Repeat ability cause to be repeated? Is it the entire effect? If I use Temporal Portal to give Find Your Center Repeat and pay the cost while its cost reduction applies, does the cost reduction happen once or twice, and does the final spell cost 2 or 4?

Repeat causes you to repeat execution of a spell’s “instructions,” which are the things the spell tells you to do as it resolves. (We’ll give a better definition of “instructions” and how to define them in an upcoming rules update.) And the Repeat cost of Find Your Center isn’t reduced, even when its base cost is, because anything that asks for a card’s cost finds its printed cost as the answer. This means that Find Your Center’s cost reduction applies only once and the final spell costs 4—its base cost of 3, plus its Repeat cost of 3, minus its cost reduction of 2.