Question

1. Can I ask you to wash the dishes?
2. May I ask you to wash the dishes?
3. Might I ask you to wash the dishes?
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What is the difference between #1 and #2? Do you use #3?

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4. Where can I find the post office?
5. Where is the post office?
6. I'm looking for the post office.
7. How can I get to the the post office?
8. Can you show me how to get to the post office?
9. How can I go to the post office?
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Q1: Are the questions all grammatical? Do you use them frequently?
Q2: What about #9? Can we use 'go to' instead of 'get to'?

Answer 1

Technically, the word "can" is asking if you are able -- that is, are you physically able to do the task. (This phrasing is often used as an alternate to "may...")

The words "may" and "might" are asking permission. #3 is not often used.

#s 4-8 are all correct and used often. #9 makes sense, but seems a bit odd.