What is the meaning of -나?

An interrogative marker in the familiar speech level; with -요 (-yo), also used in the polite speech level.

Conveys a question addressed to oneself.

In the plain speech level, an interrogative marker denoting polar (yes-or-no) questions.

Used in -나 보다 (-na boda).

Post-vowel allomorphic form of -이나 (-ina).

Post-vowel and post-liquid allomorphic form of -으나 (-euna).

Source: wiktionary.org