I know modal verbs like want, can, should etc. However, Which is the better way to ask with these verbs? I use 'Do you can?', 'Do you should' etc. Are there better way to ask with modal verbs and ask a request?
Want is not a modal verb but a catenating ('chaining') lexical verb. In questions it requires "do support" to provide a leading auxiliary which can invert with the subject:
You want to do it this way → Do you want to do it this way?
Modal verbs are never employed with auxiliary do because they are 'defective': they have no infinitive form which can act as the complement of do (or any other auxiliary. That's why a modal verb must always be the first auxiliary in a verb phrase.
And because modal verbs are always auxiliaries and always head the verb phrase, they invert with the subject in questions, like other leading auxiliaries:
Can you answer this question?
Should he come tomorrow?