"What is the name of this hotel?"
Translation:איך קוראים לבית המלון הזה?
That is related to the fact that the subject is a "dummy subject" (נושא סתמי), which is indefinite. On another perspective, think of the phrase "what is your name", or in Hebrew "what do they call you" (איך קוראים לך?). Here too, the subject is not defined, and the best (literal) English translation is "they".
Ah, you mean מַקֵּף like in בֵּית־הַמָּלוֹן hotel. It is always optional in Modern Hebrew, but it is quite common in Hebrew typography and most books and newspapers use it. You do not need it in Duolingo, because it is cumbersome to type, not being part of the elementary Hebrew keyboard.