。
I don't know if I'll have time.
Literal
Time [subject-が] exists [embedded-question-か] understand-not [polite-ません].
A clean example of an embedded yes/no question marked with か, with the matrix verb わかる ('understand'). 時間がある is the standard idiom for 'to have time' (literally 'time exists'). Subject of わかる is the speaker, omitted as usual.