For creating an NPC or Monster does the rule for adding an additional skill point or hit point per level for a favorite class apply to said NPC's and Monsters?
The guidelines for designing NPCs and creatures differ per system. It is best to look at the specifics for the system you are interested in. PF2 for instance does not build them in the same way player characters are built, rather there are guidelines and tables to help with achieve the appropriate balance for the level you are designing.
The OP is clearly talking about Pathfinder First Edition.
That said, I have always handled it that way, but only for monsters/NPCs with class levels, but as fas as I remember, there is no hard rule that codifies this.
Looking at the bestiary stat blocks for goblins and hobgoblins, it looks like they do have a favored class bonus: the goblin has taken an extra skill point, and the hobgoblin has taken +1 HP.
Monsters with no class levels don't have this (based on the one I looked at).
The Core Rule book states “Each character begins play with a single favored class of his choosing”. NPC stands for Non Player Character. That would mean that RAW an NPC does get the favored class bonus for any levels in that class. If it were limited to PC the book would have specified that. A GM is of course free to make a house rule that the favored class bonus is limited to PC’s.
