Use кљм рабћтает to ask what a person does, i.e. what a person's profession is.
You can use рабћтать + Inst. in reply to the question if it is a skilled or applied profession, but use Nominative with no verb for other professions (see below on the right), though the line between the two is not hard-and-fast. Professions for which рабћтать + Inst. is acceptable are listed below on the left.
The Nominative construction is always acceptable, i.e. Онђ — врђч is equivalent to Онђ рабћтает врачћм. (This difference between skilled professions and others has a parallel in English: we say 'He works as a mechanic' but not 'He works as a philosopher'.)
Онђ рабћтает врачћм. She works as a doctor. Онђ — бићлог. She's a biologist.
Ћн рабћтает учќтелем. He works as a schoolteacher. Ћн — преподавђтель. He's an instructor.
Ћн рабћтает мехђником. He works as a mechanic. Ћн — композќтор. He's a composer.
Онђ рабћтает журналќстом. She works as a journalist. Онђ — поіт. She's a poet.
Онђ рабћтает медсестрћй. She works as a nurse. Онђ — профљссор. She's a professor.
In modern Russian, some professions have different terms for a male and a female worker:
said of a woman: учќтельница teacher (below college level)
преподавђтельница teacher (college level)
said of a man: учќтель teacher (below college level)
преподавђтель teacher (college level)
In some professions, the same term is used for both men and women:
said of a man or a woman: профљссор professor
врђч doctor (medical)
дћктор (medical or otherwise)
A few professions have terms only for women workers; these are not normally used to refer to men:
said of a woman only: машинќстка typist
мѓдсестрђ nurse (there is no universally accepted word for a male nurse, but мѓдбрђт is used by some people)
Some professions have terms for women and men, but the ones for women are somewhat disparaging and should be avoided, even though they're often used in colloquial style and may be considered acceptable by some speakers:
said of a woman only (may be disparaging and should be avoided): продавщќца saleswoman
кассќрша cash register clerk
said of both men and women (neutral in style): продављц saleswoman
кассќр cash register clerk
When a masculine nouns is used to refer to a woman, the accompanying adjective must agree with the noun, but the verb is used in its feminine form:
said of a woman: Нђш врђч ужљ пришлђ. Our doctor has already arrived.
said of a man: Нђш врђч ужљ пришёл. Our doctor has already arrived.