I guess you are asking about SO if so, Its second officer not senior officer.
CADET:
Cadet for qatar airways can be only nationals where they will train the person from zero to PPL,CPL, ME/IR, ATPL (frozen) in the company expense. Then they will be recruit by the company for the position in flight deck.
SECOND OFFICER:
SO is the position which you can apply only with some flight knowledge, That is CPL ME/IR with frozen ATPL. Its not really some ha ha..... Company will then recruit you to some flight deck position if you are eligible. Then you will be serving the company for a while as a SO before you are becoming a FO.
Hope it clears your doubt
Cheers!!!!!!