What is the meaning of -dü?

Marks a noun as possessed; used with most types of nouns, including instruments, kinship terms, body parts, and natural and cultural elements.

Forms a noun from a verb, representing either the (nonpast) action or the object of the verb; must be accompanied by a personal prefix and an indicator specifying the role of the verb argument indicated by the noun (intransitive argument w-, transitive agent n-, or transitive patient ∅-).

Forms the imperfective aspect in many contexts.

Relativizing clitic; nominalizes a construction containing a finite verb, often to form a relative clause.

Source: wiktionary.org