Is it possible to determine a creature's maximum hit points through a Knowledge skill check or another means?
Not through a knowledge check.
The rules for the knowledge skill states:
You can use this skill to identify monsters and their special powers or vulnerabilities.
The maximum possible number of hit points a monster has is neither a special power (e.g., breath weapon, spell casting, shape shift) nor is it a vulnerability (e.g., susceptible to sunlight, extra damage from fire attacks). All monsters have hit points, so there's nothing "special" about them from an objective standpoint. A GM might give you a clue to the monster's general toughness from a successful knowledge check, but knowing specifically the maximum hit points a particular type of monster can have is beyond the scope of the Knowledge skill.
There are no other official skills, feats, spells, special abilities or magic items that reveal maximum hit points of a monster type.
You could always check the Bestiary.
Not to be flippant, but if you're going to be so meta as to calculate the maximum possible number of hit points a monster has to determine whether your character will cast a certain spell, you might as well just check the Bestiary if the GM allows it. If the GM does not allow it then that tells you something: he is seeking to limit the amount of meta information available to you at the table, and the general reason for this is to maintain an air of mystery and uncertainty for the player and simulate a lack of information available to the player character. GM's generally do this to enhance the fun of the game--the idea being that it's fun to have some uncertainty when you face a monster. The point here being that this is likely information the GM doesn’t want you to have ready access to, but if he does, then he probably won’t mind you consulting the Bestiary.
Your best bet for determining if a Power Word spell is worth casting, if you have time, is the use of an augury spell.
If a wizard is considering Power Word Kill or Power Word Stun, as you state in the comments, having a cleric cast augury and asking about that course of action should yield a solid answer as to whether or not it will be effective. This is not a way to find out a monster type's max hit points, but it does address that specific problem.