For example, in the office, a personnel commits a punishable mistake. Thus, he is placed 'under suspension'. Is it correct to say that "he is suspended" or ask "who suspended you?"? Does anyone know any proper way of saying this?

'He is suspended' is fine.
'Who suspended you?' is also fine.
'He is on suspension' also works.

bhai shahab dono hi sahi hai jache jo bolo.