You can forget about the vapor barrier, because it's already there.
One coat of oil-base paint, or two coats of latex semi-gloss,
will give a perm rating of 0.99 or better. So your vapor
barrier has probably already been painted into place.
That doesn't, however, address the penetrations of wall
openings between ceilings.

Tom wrote:

I have an older home with 6 inches of cellulose blown between the
joists of an unfinished attic. There are about 10 inches of
fiberglass batting on top of this. There is no vapor barrier.

I'm thinking of adding some more batting, but should I start over by
removing the blown cellulose first , putting in a vapor barrior and
then the batting? Or should I just forget about the vapor barrier?
There is plenty of attic ventilation and no evidence of water damage.

Thanks,
Tom