Does touching women temporarily forbidden in marriage nullify ablution?
It is prohibited to touch, or to shake hands with such women as they are considered strangers, and doing so nullifies ablution.
Does the clipping of nails nullify ablution?
No, it does not, and it is preferable to wash the hands afterwards.
How many prostrations of Quranic recital are there, and is it permissible not to offer them while reciting?
There is one prostration for the Quranic recital, and it is a Sunnah for which one is rewarded upon offering it. However, one who doesn`t isn`t punished. Therefore, those who fail to offer it aren`t considered sinful, rather they deprive themselves from the reward.
What is the ruling if someone wipes his head then shaves it - must he repeat it?
If a person performing ablution shaves his head after wiping it during ablution, he is not required to re-wipe his head or repeat the ablution. And Allah the Almighty knows best.