。
I wonder where she studied English conversation.
Literal
She [topic-は] where [at-で] English-conversation [object-を] studied [I-wonder-のだろうか].
英会話 ('English conversation') is the standard term for spoken-English learning, distinct from 英語 (the language as a whole). The Japanese English-learning industry is built around 英会話: scores of 英会話学校 (English conversation schools) cluster near major train stations, and 英会話 has come to mean specifically the spoken-fluency dimension of English study. のだろうか layers wondering with rhetorical pondering.