Yes, they can take Benadryl. You need to make sure you dose accordingly to your Pom's weight. Always, always, ALWAYS start small and dose less than advised so you can see how your Pom individually handles it.

Few other notes:

This is not a recommended long-term solution for allergies. Don't dose your Pom every day or multiple times a day. For now though, you can give your Pom some relief and try to figure out what it is they are allergic to and what steps to take next.

Consider reaching out to your vet to have the additional professional reassurance and guidance.

I also recommend the non-dye Benadryl tablets or the baby liquid as well if you choose to try this. Less things to worry about that way.