If you have a sketch that is semi-dimensioned or constrained it’s very easy to see what is left to be dimensioned. Simply pick and drag on any of the blue entities such as endpoints, lines, or arcs. Your sketch will start to move, simply hit the Undo button and dimension that particular item. Remember the sketch items colored black are already fully constrained and will not move.
Or you can use the Tools > Dimensions > Fully Define Sketch to add dimensions or relations to the under defined geometry.