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Short answer, it depends.

Little longer answer- some people will not have a p-wave at all, some will. When you try to determine P-R in those with a P-wave, it can be delayed due to multiple reasons, conduction delay, tissue scaring, congenital defects, old cardiac injury etc. Plus a wider QRS interval is normal due to the artificial signal, which would give you a much wider P-R interval.

Long answer, well, I need to ask a cardiologist.

Yup, you sure can in most cases. And its good to, as even though they have the PPM, they may still experience infarcts etc that you can pick up this way.

Depending on lead position of the PPM, you may or may not see a P-wave. You will only see a P wave if the lead is up high enough that the whole atrium does the P. If you do see a P wave, calculate it ignoring the pacing spike.

The QRS should still be seen, as this is ventricular, and should be conducted down still if the PPM is just an atrial lead.