Is it permissible, Islamically, to combine work and study in the questioner's country, along with traveling occasionally to meet the supervisor of the doctoral dissertation, and is the scholarship received permissible?

An employee must fulfill the conditions of their employment, just as someone receiving a scholarship must fulfill the conditions set by the grantor. This is based on the Prophet Muhammad's (peace be upon him) saying: "Muslims are bound by their conditions, except for a condition that makes a halal (permissible) thing haram (forbidden) or a haram thing halal." If your studies do not conflict with your work and the granting institution does not stipulate full-time dedication, then there is no harm upon you. However, if combining the two conflicts with the conditions, you must fulfill the conditions or resign from the one you cannot fulfill.