Is my interpretation correct?
A) I don’t know who Erika is.
B) Oh, she is a nurse who takes good care of me.
A) I don’t know who is Erika.
B) Oh, she is the taller of the two girls standing over there.
[1] I don’t know who Erika is . [2] * I don’t know who is Erika . Example [1] is fine but [2] is ungrammatical.
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[1] I don’t know who Erika is.
[2] *I don’t know who is Erika.
Example [1] is fine but [2] is ungrammatical.
The underlined elements are subordinate interrogative clauses. But clauses like this don't have subject-auxiliary inversion, which is why [2] is ungrammatical.
The meaning of [1] is
"I don't know the answer to