It is already a request ( polite command ) but how it doesn't end in a question mark ?
Question 17 is a courtesy question, (as defined by The Chicago Manual of Style, fifteenth edition 2003), and as such does not require a question mark:
6.74 Courtesy question. A request courteously disguised as a question does not require a question mark.
[Relevant example:] Will the audience please rise.
So it is not really a question but a polite request, as you can see from the example above which takes a more or less identical form.
Is it imperative , interrogative or what ?
I think the way in which the request was 'disguised' as a question here is what confused you, but as this is a request it is imperative.
The third type of sentence in the English language is the imperative
sentence. Imperative sentences, or imperatives, make commands or
requests. ... Periods and exclamation marks indicate imperative
sentences in written English.
Reference - Sentence Purpose - parentingpatch.com
The way you can spot that this is imperative is that it ends in a period, and is a request for someone to do something. Whereas an interrogative sentence ends with a question mark.