What happens if you try to add a device using the DE command and a device trips that is already learned? Does it take up another slot in memory?

What happens if you try to add a device using the DE command and a device trips that is already learned? Does it take up another slot in memory?

No it will not take another slot. When an endpont is added, whether through the DE (discover endpoint) command or manually using the AE (add endpoint) command, if the endpoint already exists it will not be duplicated.