Cashmere sweaters are usually expensive, so finding a moth hole can be an annoying problem. However, you don't need to throw the garment out --- there is a way to repair the sweater so that the mend is practically invisible and you can still wear it for years to come. Once you have found one moth hole, check the whole sweater carefully to make sure there aren't any more that need repair.
Take your sweater to a needlecraft or yarn-supply store and look for thread that matches the colour of your sweater. If possible, buy the softest mending yarn you can find. Cashmere is preferable if you can find it in the same colour as the garment.
Look under the collar or other inside areas of the sweater for any thread you can safely remove in order to use for mending the moth hole(s) if you can't find the right colour darning thread in stores. If you find a piece of spare thread on the sweater long enough to cut off and use for the repair, be sure to secure the area where you make the cut by tying a knot at the end of the thread so it doesn't unravel and leave a hole after you cut the extra thread off.
Turn the sweater inside out once you have your needle and thread ready; make sure you always sew repairs from the inside so that that the work isn't visible.
Thread your needle, tying a knot at the end, and begin sewing the hole from one side, picking up the broken edges of thread around the hole with the needle and joining them together as subtly but as securely as possible. Do not pull the stitch tight --- this can rip the fabric and cause the hole to widen or leave the repaired area looking puckered.
When you have stitched the rest of the hole together, tie a knot in the last stitch by threading the needle through the looped thread as close to the garment as possible, repeat this so that the stitch does not unravel. Cut the thread close to the knotted end.
Turn the sweater right side out and check the area where you repaired the hole. It should be almost invisible, with no gaps or bits of thread sticking out and no puckering in the area. If it isn't sewn properly, cut the stitch as gently as possible and start again.
If necessary, take the sweater to a professional to be repaired. Get rid of moths using natural products (such as lavender oil or camphor) or mothballs around the areas where you store clothing.