Many people don’t know what its purpose is used for

Your sentence is understandable, but it’s a bit redundant in English. Here are some clearer versions you can use:

Corrected versions:

1. “Many people don’t know what it is used for.” ✅ (most natural)
2. “Many people don’t know its purpose.”
3. “Many people don’t know what its purpose is.”
4. “Many people are unaware of what it is used for.”

Your original sentence “Many people don’t know what its purpose is used for” repeats the same idea twice (purpose and used for).

If you want, I can also show you when to use “purpose” vs “used for” in English—many learners confuse this. 🙂