a. xxx 有什么意思? You ask this for several definitions of a certain word.You might also say“XXX有几种意思？”/“XXX有哪些意思？”Most of time,we use"有什么意思"when we think something is totally boring. e.g. When you see your friend is doing puzzles,and you say"这有什么意思."It means you don't think it's interesting at all. b. xxx 是什么意思? This is the correct way to ask "what does it mean". e.g. 这个词语是什么意思？/What's the meaning of this word? When somebody did something or said something which you think they had another purpose by doing that or saying that,you can use"你这是什么意思？"/"你这话是什么意思".

Both 是什么意思 and 有什么意思 mean "what is its meaning." 有什么意思 can also mean "is it interesting."

b.

you'd better say "XX是什么意思", if you want to ask 'what is the meaning of xxx' , when we say "XX有什么意思？”, it means "this is boring!!, I am not interested in it!, why you like it??!"