Why are cDNA libraries considered so valuable?

Answer to q. 1

With a cDNA library, the gene product can be expressed in a prokaryote. If the regular eukaryotic
DNA is inserted into a prokaryote, the prokaryote will not be able to process and remove the introns.

Answer to q. 2

If doctors could access their patients genetic profile, there are two primary benefits that could result.
First, the doctor could see what conditions they are predisposed to. As a result, they could both
suggest behaviors and/or prescribe medicines to potentially avoid the condition. Second, they could
determine which medicines and treatments would be most effective should the condition result

I hope they're paying you for this because all of them were correct

not really, just a volunteer... and you're welcome