Sand away the cat urine stain with medium grit sandpaper. Wipe away the residue with a tack cloth. (See Reference 2.)
Use painter's tape to outline and protect the floor and wall surrounding your baseboard. (See Reference 2.)
Apply fresh paint in light strokes across the grain of the wood then apply paint in one long stroke with the grain of the wood. Allow the paint to dry. (See Reference 2.)
Once the paint has dried, apply a clear sealer or varnish to the wood using a disposable foam brush. Again, work across the grain in short strokes then with the grain in long strokes for a second coat. Allow the varnish to dry. (See Reference 2.)
After the varnish has dried, remove and throw away the painter's tape. (See Reference 2.)