according to the falcon guide for yosemite, the total distance of the PCT in the park is 79.4 miles from donohue pass to dorothy lake pass. there is no trailhead at either end. the only road crossing w/in the park is at tuolumne meadows.
coming from the south i would get on at reds meadow which is about 20 miles south of donohue pass. that way you can take in thousand island and garnet lakes and banner and ritter peaks. other trail heads to consider would be at silver lake about 13 miles south or agnew meadows about 17 miles south. i would come in at reds meadow also because you could leave your car in mammoth lakes, where you can also pick your permit up from, and take the bus to reds.
there are several trailhead options on highway 108, one of them being sonora pass, where the PCT crosses about 18 miles north of dorothy lake pass. there are some other trailhead of 108 that connect with the PCT, but since you want to hike the PCT i would just end at sonora pass. you should have no problem hitching back to mammoth lakes from here.
the nat’l geographic trails illustrated yosemite map has the PCT north to sonora pass. as far as maps south of donohue pass, i have the tom harrison JMT map set.
have fun.
jerm