Can old detachable lens be used on new cameras?

My mom has an old attachable flash that she used for her SLR back in the day. However it in in a deep place that would take a lot to get it out. So would that flash work on my Nikon D5000?
She said it was one where it could go on any major brand back in the day.

Your question is somewhat confusing, as you first refer to a lens and then to a flash.

If you know the make and model of lens/flash, you should check on the Nikon website. The answer might be found there. If you don't know, you will probably have to dig it out.

If it is a lens you are asking about, the auto focus would not work. D5000s do not have auto focus in the camera body, and consequently need a lens with an AF motor.

A flash stands a good chance of blowing up your d5000. Here's a list of unsafe and safe flashes and how to measure.http://www.botzilla.com/photo/strobeVolts.html