This is the 277th most frequent Hungarian word.
tudják
"They know" (third person plural, definite conjugation).
In this sentence, 'tudják' is in the indicative mood, expressing knowledge possession by a plural second/third person subject.
Tudják, hogy miért fontos a tanulás.
They know why learning is important.
Here, 'tudják' is used to express the subject's understanding or realization of their desire or plan.
Remélem, hogy már tudják, mit szeretnének.
I hope they already know what they want.
In this context, 'tudják-e' forms a question, indicating inquiry about the knowledge state of the subject.