Translation:Where is your mother?
It's pronounced はは if you're talking about your own mother, but not addressing her. So if you were saying "Where is my mother?", "母はどこですか" would be acceptable, but, as far as I understand, you can never use はは for someone else's mother.
That said I only had Japanese at college for 3 semesters, so if someone actual has some real life experience, it would be appreciated if they chime in.
Don't use おかあさん for your own mother when talking to others though! It's an "in-group/out-group" distinction: Just as you must not use honorifics to describe yourself, when speaking to someone outside of a certain "group" you belong to (like your family) about someone else from within that group, the "in-group" person is treated like an extension of yourself and therefore you must speak humbly about them also. Therefore in this situation おかあさん (honorific) becomes "your mother", while はは (humble) is "my mother". When speaking to your mother directly however, the in-group/out-group distinction changes; you now need to humble yourself, but treat her with respect and say おかあさん. I hope this makes sense!
Isn't this similar to the example with parents? When talking about my parents, I (mostly) do not include honorific prefix ご, I use it when talking about other's people's parents. There was such an excercise here in Duo, where Duo did not accept 「ごりょうしん」, it wanted 「りょうしん」。
Also, in this example, I see the honorific お, so it means "your mom", but not my mom.
Is this right way of thinking, or it cannot be generalized like this?
Some of you guys are not thinking correctly about this.. kanji isn't really about how kanji is pronounced (1), it's about what the kanji means. As for 母, it means "mother", this is language independent. So you include 母 in any "word" which refers to "mother" in some way. In Japanese there are some variant words which all mean 'mother'. used in different contexts. 'haha' is what you use to talk about your mother (and that answers a couple of the questions in posts below), and 'okasan' is how you address your mother directly (and also how you talk about other people's mothers). In English and other languages you also have a number of words which all mean 'mother' (Mom, mother, mommy, etc), and for 'father' you have at least 'father', 'dad', 'daddy', and various regional and cultural variants. In Japanese you have similar variations for 'father', although in which exact context you use them may be more formalized. To indicate that these words all mean 'father' in some form you include 父 as part of that word. So it's not at all about how 母 and 父 are "pronounced", it's about how the words where you use them are pronounced. Although it so happens that just 'haha' and 'chichi' are written as the bare kanji.
in this and many other cases
not using honorifics when referring to another person's mother (in front of them) is considered rude most of the time.
So because you want to be humble to show that you are respectful to the listener, what usually happens is that you don't use honorifics for your own family.
「お母さんはどこですか？」will probably be understood "where is your mother?" most of the time because of that...
and「母はどこですか？」will almost always be understood as "where is (my) mother?".
Obviously, this also depends on context, and the relationship between you, the listener and the listener's mom.
The other sentence was probably「あなたのお母さんはどこですか」because of what I just mentioned.
I've noticed that in general お母さん usually refers to someone else's mother as it is more polite with the お prefix and the さん suffix. On the other hand, 母 usually refers to one's on mother. Therefore, because お母さん usually refers to someone else's mother, the subject is usually not explicitly stated because it is already understood.