How often do I need to re-tip the claws on my engagement ring?

On pendants probably never as they don’t have much wear and tear.

On rings it is a good idea to check the claws regularly as they can move out of alignment from a knock and may not be holding gemstone securely.

Re-tipping is not required usually for at least 10 years.   Use a magnifying glass to check on claws clearly.

When one claw breaks off then it is a good idea to do all of them at the same time. The gemstone is removed and new claws soldered onto the setting and the stone replaced.  It does not weaken the setting at all.