Let's talk about forming the possessive singular of nouns by adding an " 's "
It is a common misconception that an apostrophe s is not added to proper names ending in s (ie. Charles) but just an apostrophe following the s already in the word (ie. Charles'). This however is not the case. Proper grammar dictates that the apostrophe s is added after all proper names. The only exceptions are ancient proper names such as Moses or Jesus.
Also, be careful of it's/its. The first is a contraction of "it is" and the second is possessive. For example: "A dog must learn to scratch its own fleas" is possessive. Whereas, "it's impolite to steal" is the contraction. If you're ever unsure of which to use, simply say "it is" where you're placing the "it's" and if it makes sense, you're good. If it doesn't make sense, use the possessive.