|Question:||I wonder whether you should not see someone who could help you.|
|Lesson:||EnglishLingQ - Eating Out, Part 12|
"I wonder if you shouldn't" makes it into a slight suggestion.
It's like saying "why don't you", "it wouldn't hurt to", or "there would be no harm in seeing someone who could help you".
As you can see, Mary responded to it by asking Peter if he knows anyone who could help her.
It would be more natural to say "it isn't that easy", or to place stress on 'not': "it's not that easy".
It's the same with this sentence. "I wonder if you shouldn't..." sounds much more natural and is completely fine grammatically. Consider the sound of "I wonder if I shouldn't just say it like this". It's a perfectly colloquial expression.
I guess the reason they aren't using contractions is to teach each separate word before contracting them. I don't know. We never speak like that. I've never said "I do not know".