Russia most likely designed and built that reactor and the others in the country, back when it was part of the Soviet Union. I think it's safe to say they fully understand and are capable of operating nuclear reactors like it.
edit: Construction started on it in 1980. This is a Soviet designed and built reactor. Russia should have no problem maintaining it.
It is highly unlikely there are be nuclear scientists with that knowledge amongst the armed forces currently invading Ukraine. The type of reactor may be known but each reactor and its instruments, controls and protocols will be unique in some way. The only people who are qualified to run this reactor safely are the staff who work there every day.
It's not impossible, though. Russia seems to have pressed a lot of civilians into service. Ukraine recently captured an entire squad of school teachers.
edit: Construction started on it in 1980. This is a Soviet designed and built reactor. Russia should have no problem maintaining it.