is there any way to know when už means yet vs when už means no longer? maybe it depends on tge placement in the sentence? or should it just be obvious through context?
It depends mainly whether the question is negative and when it is positive. You will find more in other discussions here or in the recommended resources.
I THINK "už" generally means "no longer" when the verb is negative. When the verb is not negative, there's the other question of when it means "yet" and when it means "already"... :-)
Try coming at it from Spanish. "Už" and "ještě" are like "ya" and "todavía".