If you're presently in Qatar on a work visa, or have left and terminated your employment in Qatar w/in the last 2 years (employment ban duration), you need to have an NOC from your present sponsor to transfer or for a new employer to secure a work visa in the latter case.

To be considered legally employed in Qatar, you must have a work visa. Working while on business or visit visa is not legal, irregardless of what your new employer tells you. Though many expats work in Qatar while having this type of visas, this is still not legal and you are not covered by any insurance at all.

Work visa and RP are one and the same.

However, if you are eligible to be on family/dependent visa, you are allowed to work in Qatar.