In Damus:

Profile -> Edit -> Lightning address

This is your receiving address which must be a LNURL address (like an email address). Best wallets are of course non custodial wallets like Zeus, Phoenix or Mutiny. However, they often come with some fees which is not optimal for low zap amounts.

On getalby.com you can easily create a lightning address, which you can add as receiving address. But be aware, this is custodial and therefore only suitable for low amounts.

You can employ the same receiving address for multiple accounts, provided you don't mind it being apparent that these accounts belong to the same owner.

Settings-> Zaps -> Wallet

This is your sending lightning wallet which may differ from your receiving one.