Whenever I finish a digital painting, I like to do a few last-minute touch-ups and fixes in Photoshop. You can resize your image, adjust colors, etc. We're just going to do a few minor tweaks to our image now that the painting is finished.
Open up Photoshop and open the PSD file that you saved in Painter.
Example
Sometimes it's nice to add a few bright sharp highlights to some areas, like a wet nose, hair, or eyes. Select the Dodge tool and make sure a hard-edge brush is selected and that "Range" is set to "Highlights."
Example
Select the Color layer (not shading layer) which you wish to add highlights to and color with the dodge tool as if you would with the paintbrush. You'll notice the area you color in is brightened.
Example
Do this in any areas you like. For this image, I added highlights to the nose, tongue, did a few strands of highlighted chest fur and brightened the light part of the iris.
Example
Last, the final highlighted touch: the shine in the eye! For this you'll need to make a new layer, above everything else. We want this light to be a nice pure white, unfettered by any of our shading. Simply use the paintbrush tool and paint a solid white highlight.
Example