I would say the user who is uninstalling your application isn't in a mood he is willing to answer to a lot of questions. He already wasted too much time downloading and trying it out.
-> You have to be short if you want to get any answer.
Thus, you can't choose a usability scale survey and anyway you would get an overview of your application but you won't have any specific information about what exactly the user tried to do and what are the real issues you need to correct.
It's going to be difficult to detect what are the issues with a few questions so you should make an open question about what did he want to do and what went wrong or what didn't he like. Start the survey explaining that his feedback is valuable to you and it's gonna help you improving your application.
Example:
Please take the time to help us improving our application.
Tell us what did you want to do and what didn't you like.
-------- Text Area --------------------------------------------------
4/6 lines to answer, keep it visually short, we don't want the user to think we expect him to write a lot.
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Thank you for your answer. (on send)
Should you ask for his email ? I don't think so, keep it anonymous and they won't feel bad giving negative feedback...