In Jain tradition, you usually know your gotra from your family lineage, elders, and sometimes from community or marriage records.

Common ways to know it:

• Ask your parents, grandparents, or family elders
• Check family documents or marriage papers
• Ask your Jain community/mandal
• In some families, the surname or ancestral village also gives a clue

If you mean gotra in the spiritual Jain sense, then it is also related to karma and birth lineage, but for daily and social use, people usually mean the family gotra.

If you want, I can also explain the difference between gotra in Jain family tradition and gotra karma in Jain philosophy.