I didn't knew about it.
or
I didn't know about it.
or
I didn't know about it.
Grammar!
<<I didn't know about it. >>
Around here, most folks would prefer this form over the other one.
Around here, most folks would prefer this form over the other one.
eeuuian is being too equivocal: the first form is completely ungrammatical in all dialects of English. It would have to be "I didn't know about it". (After the auxiliary verb "do [not]", you have to use the bare infinitive, "know".)