。？
The story of those Seven Wonders — you looked into it for me, right?
Literal
In-question [attributive-の] seven-wonders [attributive-の] story. Looked-into-[come-てきた] [nominalizer-の] [polite-でしょう]?
件の ('(the) X in question, the aforementioned X') is a literary attributive used to refer back to something previously discussed. Similar to English 'the said' or 'the aforementioned.' 七不思議 ('Seven Wonders') is a common trope in Japanese schools where students identify the 'seven mysteries' of their school — often supernatural.