Showa that there were suspicious circumstances surrounding iqbals final night

That his dad gave him is the adjective clause in the sentence.

Adjective clauses all modify nouns, and usually come after the noun they modify. 

In this case, that his dad gave him is modifying the knife.

Random note, adjective clauses usually start with words like that, which, who, and other pronouns like that, and it will also have a subject and a verb.

Source: Really great Language Arts teacher