Is there any way to find your own Taiwan pass number?

Inquiries can be made by telephone or in the service hall of the Exit-Entry Administration Office of the public security organ that handles the Taiwan Pass.

If you need telephone consultation, you can check the specific telephone number through the online service platform [office] of public security entry and exit.

References:

Public Security Entry-Exit Online Service Platform

Guidelines for registered residents to handle mainland residents' travel permits and endorsement services to and from Taiwan