Mogen Sie Hunde? Isn't Sie when together with Mogen - They like instead of You like?
Mögen Sie Hunde? = Do you like dogs?
Mögen sie Hunde? = Do they like dogs?
The difference is the capitalization of "sie"/"Sie".
Danke, Katherle! Here's a Lingot for that explanation! "Magst du Hunde?" would also be correct, wouldn't it? I went to Google Translate to see if I was correct with "Mögen sie Hunde oder Katzen?" and it changed from you to they as I typed "oder Katzen". Now I know why.
Yes, it would be. But as you can see, the exercise proposed is about formal sentences. So in this context the proper pronoun to use would be "Sie".
The verb conjugation for Sie (you formal) is the base form of the verb. You should refer to the verb conjugation tables for more information.
Although not proper, it is common in English to drop the 'do' and say 'you like dogs?' rather than 'do you like dogs?'. Is 'do' to be used always in German?
We use US English here and do is sometimes dropped (or rather, unpronounced) in informal conversations. But for polite or formal conversations, do is not dropped as it is standard English.
I'm not sure if the same rule applies 100% when translating these German sentences but since we're learning standard German, it's better to keep the do.