I know about the examples given of "the man kissing the woman" or "boy kissing the girl". My question is, how do I use the -n if the object ends in, for instance, the letter n as in John, or in y as in Mary? Do I add an o and then the n? Do I just add the n by itself. How would you even pronounce the word Maryn?
My perception is that the most common thing to do is just to not bother marking the object, so in your example it would just be something like “John kisas Mary”. Even though Esperanto has a flexible word order, the default is subject-verb-object like in English. When it is not possible to mark the object you can usually just rely on this default to be understood.
For a more complete answer, see this similar question: What is the best way to express the accusative of non-Esperanto words in an Esperanto text?
I often try to rephrase things so that the accusative isn’t required on a non-Esperanto word or name. If all else fails, there is always the passive.
John estas kisata de Mary. (John is kissed by Mary.)
Mary estas kisata de John. (Mary is kissed by John.)
I don’t believe it is common, and some will likely call it bad style.