1.D.
用不定式做后置定语,修饰a good place.
2.Jim can't decide what he should do next.
=Jim can't decide (what to do) next.
“疑问词+不定式”结构相当于一个名词短语.
3.I really don't know what I'll say to him.
=I really don't know （what to say）to him.
另：“疑问代词+不定式”结构中,疑问代词会充当后面不定式中某个动词或介词的宾语,如：
what to do what是do的宾语
what to say to him what是say的宾语