What is the meaning of -nak?

to, for

's, of (forms the possessive from the noun of the possessor, along with the ending -a/-e/-ja/-je added to the possession. Often omitted if the act of possession is not the predicate of the sentence.)

Indicates the second, predicative complement of several verbs, e.g. those with a sense like call, name, find, deem, judge (appellation or appraisal)

as, for (in the function or role specified)

Forms the concessive sense: used to devalue the predicate of the sentence when repeated and followed by a clause that contrasts with or contradicts it. See also -ni.

Forms the third-person plural and formal second-person plural present tense (indicative mood, indefinite conjugation).

Fused enclitic with second-person singular agent and first-person singular patient; fuses -mo (you, your) and -ak (I, me)

Fused enclitic with third-person singular agent and first-person singular patient; fuses -na (he, she, it, his, her, its) and -ak (I, me)

Source: wiktionary.org