I'm saying
How many times I asked you not to do that?
or
How many times I asked you to not do that?
which one is correct please?
Neither is completely correct: you can use
How many times have I asked you not to do that?
or
How many times have I asked you to not do that?
Notice how the word "I" is capitalised in English. This is always the case.
The word "have" is required as an auxiliary verb to form the present perfect with the past participle "asked" for it to make sense in those sentences.
Both "not to do" and "to not do" are correct.
How many times did I ask you not to do that?
How many times did I ask you to not do that?
The first sentence, in which we keep to and the infinitive do together, is more usual and idiomatic than the second sentence, in which we have a split infinitive. Many people think that a sentence with a split imfinitive is not correct, but it's becoming generally acceptable.
The only difference can really be seen when you say the phrase.
How many times have I asked you NOT to do that?
vs.
How many times have I asked you to NOT do that?
The emphasis is always put on "not".