Is it from the Sunnah for the suitor to ask his fiancée about her virginity, and what does the Sharia obligate him to do if she is not a virgin?

It is permissible for the suitor to stipulate virginity at the time of the marriage contract. If he marries her and finds her not to be so, he has the option to keep her or to divorce her. However, if he did not stipulate this, or if he knew of her non-virginity, then he has no such option. The question of virginity is not a Sunnah (definition), but rather it is permissible at the time of the marriage contract. The Sunnah is to encourage marrying virgins.