"Aamir can study."

Translation: आमिर पढ़ सकता है।

[Signorellos]

है - Is it necessary?

[vinay92]

Yes. You can think of it as marking the present tense.

[Sunnymonie]

Does sakna has special deal with verbs
so we use only the root form?
Because when we use chahana the verb come in the infinitive form
आमीर पढ़ना चाहता है

[vinay92]

Yes. It's because 'sakna' is an auxiliary verb and is only used along with other verbs.
'Chahna' is a regular verb and the other verb (in the infinitive form) takes the place of an object.

It's a similar deal as with 'can' and 'want' in English.