Is it possible for an adult to inspect his own milah to determine if the milah was done in a halachically proper manner? Are there any picture guides or some other type of resources that would help someone who is completely ignorant in the details of what a bris milah entails, to educate himself to the actual practical details of the laws and in turn allow him to inspect his own milah?
When inspection is helpful, self inspection is good enough. For negayim, a man cannot check his own negayim, but for most isurim a man can check himself for shechita, Kashrut and all isurim.
There are a lot of question around a circumcision as other users have said.
We will try to answer a few of them.
If residues of foreskin remain, have we to cut them? The Shulchan Aruch says in Yore Dea siman 264, se'if 5, that if in some place a residue of foreskin covers the majority of the length of the glans, even in a small area, he still needs to circumcise as if he was not circumcised. The Baer Heytev (in name of an opinion reported in Bet Yosef and Shach) adds that if the majority of the circumference of the corona glandis is covered, he is not regarded as circumcised. This part of the inspection may be a self inspection.
Is it important to know who was the Mohel? The Shulchan Aruch in 264, 1, said that even a child or a woman can circumcise, bediavad even a NJ makes a valuable circumcision. But Rama requires brit bloodshed.
The time of the Brit. Rama at the same place explains that a child who was circumcised before his 8th day of life needs also brit bloodshed.
For 2 and 3, I am not convinced that a Jew needs to investigate to ensure that the conditions was fulfilled.