From wherever you choose to park in the vicinity of Clear Lake, walk on up to the lake and then follow a trail around the east end that heads up toward the saddle on the long connecting ridge between V.5 and South Lookout. There is a rocky summit west of the lake that is mistaken by some to be South Lookout. It is not. It is a "soft-rank" summit however and a worthy climb if you have the time. The true summit of South Lookout is NW of the lake and not actually visible from the lake or on your way up.
After you have followed the trail to the saddle up for some distance, begin to veer away to the NW and hike up through lush displays of wildflowers toward the false, south summit of S. Lookout. The hike all the way up will be mostly on grass & tundra, with some soft scree as you near the false summit. It will take most of an hour to reach the false summit, which is unnecessary to go over. The easy strolling is now over. The survey map gives no indication of what lies ahead.
The true summit of South Lookout, when examining the USGS quad, is the middle of three high points. The north point shows an elevation of 13,357 ft., but this is not the highest point, which is found on the middle summit. In attempting this peak, we had a few sources of beta. I believe the route we took was not described on any of that other beta. The others seemed to have you contour farther along the east face of the peak than what we did. I believe our route provides a shorter, but not necessarily any easier approach to the summit. The climbing required is not difficult, so we rate it at 4th class, but loose rock and some exposure may make this seem as 5th class.
If one proceeds directly north along the ridge crest, from the false, south summit, you will not get far before being confronted with a vertical wall of rock. There is no apparent way to circumvent this wall on the west side. All the information we had indicated the way to the summit was on the east side, and we could see why this was the prevailing opinion.
Our plan then, was to follow the sketchy directions we had from a couple of sources.
From the east side and below the false summit, we began by hiking at a descending/contouring angle down the east flank of the mountain, crossing one branch of a larger couloir, then a very minor rib of rock and entering the second branch of the wide couloir. We continued angling down and arrived at a vertical wall of rock that halted further progress north. Total elevation loss to this point was less than 100 ft. and one could have easily scrambled directly up and have been back on the south ridge. At the wall of rock that confronted us, we continued to descend some until we came to a place in the wall that was not so vertical and appeared to offer a scrambling access to whatever lay above. Ascend on up the receding rock layers above at this breach in the wall. A 4th class scramble of about 30 vertical feet will bring you to a small perch where you can change direction toward the left and cross over the crest of the rib. If using a rope, there are a couple of spots where you can belay others up here. On the rib crest, peer into an extremely steep gully just a few feet away. A rock ledge, about 4” wide and 3 feet long leads into this narrow gully. Enter the couloir. It is so narrow, you can stretch out your arms or feet and touch both sides. It was almost like a near vertical slot canyon. Earlier in the season, it would most likely be filled with snow and require the security of an ice axe to cross. Exit the couloir at almost the same level at which you enter, scrambling up only a few feet to find a good exit point. Walk out onto the more stable and secure slope above the couloir and perhaps find a faint trail. There may even be a cairn. Hike NE along the slope of rock ledges and tundra, cross the next minor ridge and then ascend west in yet another flat scree-like slope to a flat area immediately below the middle summit block. From here, it's just another easy, 3rd class scramble to the summit on secure rock. We did not use rope on this ascent, however, in returning to this same route in 2013, we did use rope, in part for the sake of another party member who was not at ease with the exposed scrambling, but also because it just felt better to have it on the many loosely perched rocks you have to scramble over. If taking rope, you don't need more than 100 feet and some sling to set up an anchor.
From the summit, you have an impressive view north of the long east-west running ridge of Silver Mountain, San Joaquin Ridge, etc. To the west, US Grant offers an imposing east face. And then to the SW, the summits around Ice Lake Basin are visible. The views are quite impressive. To return, going back exactly as you came is the safest bet. If you have time, consider tagging the soft-ranked summit west of Clear Lake. It makes another interesting climb without the fear factor of South Lookout.
Links to other information, routes & trip reports for this peak that may be helpful.