What's the name of the folk song that Tsuji was singing in the drama?
Literal
Tsuji-san [subject-が] drama [possessive-の] inside [at-で] singing-was folk [possessive-の] song [topic-は], what called [copula-ですか]?
フォークの歌 ('folk song') uses the English loan フォーク. ドラマのなかで ('in the drama') sets the media context. 歌っていた is the past progressive of 歌う. 何ていう ('what is it called') is the casual form of 何という. A straightforward media/entertainment question.