A doctor needs to be a specific speciality to treat cancer patients.

[tufguy]

1) A doctor needs to be a specific speciality to treat cancer patients.
2) Doctor Smith is a different speciality than gastroenterology.
3) What speciality is dr Smith?

Have I used speciality correctly?

 

[Tarheel]

A doctor who treats cancer patients specializes in oncology and is an oncologist.

Say: "What is Dr. Smith's specialty?"

 

[Tarheel]

A doctor is not a specialty.

 

[PeterCW]

In the UK the genetic term for a doctor who specialises in a specific subject is "specialist". We would say "a doctor needs to be a specialist to treat...".

For your last sentence a native BrE speaker would probably say "What does Dr Smith specialise in?"

Please note the use of upper case when using titles as part of a name.