Unless he is using 8.2 you can't do snapvault inside a vfiler. The volume can be owned by the vfiler but vfiler0 has to own the snapvault relationship.
the command is simple, "snapvault snap sched -x sv_daily 7@23@sun-sat". The -x flag says update the snapvault from the source and then create the snapshot sv_daily.0. If you simply want to create a snapshot, leave the -x flag out. We do that for things like weekly snapshots, "snapvault snap sched sv_weekly 52@23@sun" This just creates it without updating, useful if you are doing daily updates already.
Re: Snapvault snap sched is gone for no reason, how to reschedule?