What does she want to know? CORRECT
In this sentence the auxiliary verb (helping verb) do (present tense) must agree with the third person subject she and the main verb want following the auxiliary verb must be in the bare infinitive form (i.e., the infinitive without the to)
e.g.:
I do like...
You do need...
He/she/it does work...
We do like...
You do need...
They do work
What does she wants to know? INCORRECT
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He doesn't seem happy. CORRECT (same rules as above)
He doesn't seems happy. INCORRECT
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