Questions & Answers about Твоя квартира в новом доме?
Why does the adjective have an -ом ending in новом?
The adjective describes доме, which is in the prepositional case because it follows в (in) to show location. For masculine nouns like дом, the matching adjective ending in the prepositional case is -ом. This turns the basic form новый (new) into новом.
Why didn't твоя (your) change its ending to the prepositional case too?
Твоя describes квартира (apartment), not the house. Since the apartment is the main subject of the sentence (the thing that "is"), it stays in the basic dictionary form (nominative case). Because квартира is a feminine word, we use the feminine form твоя.
Does дом mean "house" or "apartment building" here?
It means "apartment building" in this context. While дом is often translated as "house" or "home", Russian uses it for residential buildings of any size, including large multi-story apartment complexes.
Where is the word for "is" in this sentence?
Russian usually leaves out the verb "to be" in the present tense. To ask "Is your apartment...?", you just state the facts and use a rising tone of voice. In writing, the question mark is the only thing that separates this from the statement "Your apartment is in a new house."