Student or Learner
Dear professor: Could you please explain the difference between I wondered that..., I had wondered that... and I was wondering that... in relation to tentativeness or politeness?
I think you're getting at "I was wondering if I might trouble you for the salt?"
Regardless of how you say it (I wonder if, I was wondering if) it is still a present-tense request. The "was" just serves to stretch out the phrase, and there is a concept that if it takes you longer to say it, it must be more polite.
Pass the salt.
Pass the salt, please.
Would you please pass the salt.
Could you please pass the salt, if you don't mind.
I was wondering if you could please pass the salt if you don't mind.
The wondering part would be more likely as
I was wondering if there is any salt on the table? (that's a polite request: pass it)
I wonder if there is any salt on the table. (That's not a request, so much as an observation of the lack of salt).
Now, as for the I wondered / had wondered that/if - that would have to be in an entirely different context; I don't think it fits with your question regarding tentativeness or politeness. To say "I wondered, or had wondered, if you could pass the salt" would suggest a retelling of a situation that happened yesterday. You no longer wonder, and no longer need the salt.