In spoken German emphasis is more a matter of intonation than of word order.
In your example sentences
Wir spielen heute Tennis.
and
Heute spielen wir Tennis.
it's not really clear, what sentence emphazises what part of the sentence just from word order.
You wouldn't ask:
Ist es ein Büro, in dem du arbeitest?
The grammar is correct but you just wouldn't talk like this. Instead a native speaker would just ask:
Arbeitest du in einem Büro?
and emphazise Büro by intonation.
Let's use another example: Two people meet somewhere in a company building.
A: Wohin gehst du?
B: Ich bin auf dem Weg zur Kantine.
A: Arbeitest du in der Kantine?
Here it's pretty clear. A is asking B, if B is working in the canteen or having lunch ... So A would probably stress arbeitest by intonation.
Now let's imagine, A knows B for a while but they didn't speak for a while. A knows, that B is really good in cooking but wouldn't expect B to work for that company because B was never really interested in the companies field. Now A is asking:
A: Was machst du denn hier?
B: Ich arbeite hier.
A: Arbeitest du in der Kantine?
Even though A is explicitly asking for the place here, A would never change the word order just to emphazise Kantine.
Ist es die Kantine, in der du arbeitest?
Ist der Ort, an dem du arbeitest, die Kantine?
No native speaker would ever do that. A would just stress the word Kantine by intonation.