From a smart contract on Base, how can you look up an ENS onchain for a given address?

@day---break, day---break.com // nf.td/iam

Like a Basename? I think you could do that through the Resolver on Base. If you're trying to bridge an ENS on mainnet you might need an offchain gateway

DX Engineer | Head of Developer Relations at /pinata | Building orbiter.host | stevedylan.dev/links

Hoping for both. ENS, with a graceful fallback to Basename, then address. 

fname might be a better option for this

You can definitely make it happen by following some resolver examples, but it would require some offchain API work to bridge Base with Mainnet. That's what we had to do with Orbiter, and it's technically what Base does with Basenames to a point