Proof of time in germany with german working holiday visa

I am wondering when i leave germany just before my visa expires, will I be asked to prove the amount of time I spent in Germany as opposed to other shengen countries?

No, at least, I have never heard this happen.

Or will I not be questioned as i have the visa?

That's the most likely scenario.

If you exit directly from Germany you'll be fine.
It's the other Schengen states which may ask questions or even make trouble if it seems due the stamps in your passport or the entries in the Schengen Information System (a database) that already overstayed your 90 days in the Schengen area (apart from Germany).

Better is when traveling on such a working holiday visa to cross the outer Schengen border only (or at least mainly) to/from Germany. Which means: by (budget) flight - as Germany has no common borders with non-Schengen states.

There is no rule that I'm aware of that you have to prove how much time you stayed in the country which issued your visa, so why would they ask for that?

It also doesn't matter where you enter and exit the Schegen zone, and I see no reason to exit via Germany if it isn't convenient for you. The whole thing is made to make travel easier, not more complicated.

Having said that, you should be prepared to answer questions and know which countries you visited and when, and which mode of transportation you used to get to country X to Y during your entire stay.

let's turn the thing around- if somebody had a WHV for Germany and spent all their 7 months in Germany, not setting foot in any of the other Schengen countries at all.

How could they prove that?

They would have no tickets in and out of Germany, or hotel receipts to show. The only way to prove would be to keep receipts for every day they were in Germany, 7 months long. That would be absurd. You would have to carry a whole admin file just to prove that you didn't leave.

The most they could ask for is to make it credible you spend most of your time in Germany- e.g. proof of a job, long-term accommodation. Of course, nobody says you need to stay in the same place for 7 months and you may have stayed with friends, and you may not have find a job, so but you should be able to give some kind of explanation what you did. That's all.

I also don;t think it matters where you exit Schengen- as long as what you're doing is legal you should have nothing to worry about. If you exist Schengen outside Germany just keep proof that you were still in Germany less than 90 days ago, so nobody can accuse you of overstaying.