Pictured is a simple bicycle wheel truing stand that was made from scraps around the workshop. The uprights are made from 1 X 3/8" bar stock, and cut at 45* at the top, joined (welded) to short lengths of 1 X 1/4" notched bar stock to intercept the wheel axles. Square tubing (sliding fit) allows the width to be adjustable and provides a place for mounting, either on a work bench or in a vise. In use I hold a piece of yellow chalk against the rim and spin it to find the high spots. Then make the necessary spoke adjustments. If you wanted more accuracy, you could mount a dial indicator on a leg for that, but I have found that the chalk method is good enough for my needs.
Close up of fork details.