Is it permissible to remove the niqab — which the questioner considers recommended, not obligatory — for the sake of work or study in a rare and beneficial specialization for the Ummah, knowing that it is absolutely rejected in the travel requirements for European countries?

The covering of a woman's face is a point of contention among jurists. The preponderant opinion is that it is obligatory. Therefore, it is not permissible to remove the niqab for the sake of work or anything else, except out of necessity or dire need. If there is a dire need for study, and it cannot be achieved except by uncovering the face, then it is permissible to take advantage of this concession only to the extent of the need, and covering it becomes obligatory once that need ceases to exist.