Tone ring is behind the hub. Easier to replace the entire hub.
Sensor is the line to the brake and goes to the lower part of hub.
Once you look, you'll see it. There are only two lines there, one is a brake line.
Have you lost a lot of fluid lately?
Bleeding an ABS unit is not something most of us can do, if that is your problem.
Google subaru abs malfunctions and you'll have a starting point.