What is the ruling on adding to a CV a course that was not attended, but its videos were watched and no certificate was granted for it? And what is the ruling on adding skills that have not been practiced before?

One must be truthful in what one reports. If someone has watched video materials of a course, there is no harm in mentioning that in their CV. However, claiming to have participated in the course and completed it is a lie. Similarly, claiming mastery of skills one does not possess is a forbidden lie.