You have to pay attention to case (nominative vs accusative, etc.) and number (singular vs plural).
Hungarian uses suffixes to indicate case and number, the suffix for plural for example is -k, like here: sportoló is singular, but sportolók is plural.
Same goes for case: When something is an object of an action, (like the object of e.g. eating), that is accusative case. The suffix in Hungarian, for objects in accusative is -t, for example: I eat an apple. = Almát eszem. (a in alma becomes á solely because of pronunciation reasons).
Now the question words must agree in case AND number with the subject/object of the sentence. So like in this sentence, where we are talking about sportolók which is a plural, nominative noun (nominative being not accusative or else), the question word must be plural too. The singular question word for what ... like in Hungarian is milyen, therefore its plural counterpart is milyenek (the reason it's -ek and not simply a -k is for pronunciation reasons, also consider vowel harmony)