So what can
one make a dominated PC/NPC do? Avlis' Wiki has an abridged description from the Player's Handbook for Dominate Person:
Avlis Wiki wrote:
The caster can control the actions of any humanoid that is Medium-size or smaller. The character establishes a telepathic link with the subject’s mind. If a common language is shared, the character can generally force the subject to perform as the character desires, within the limits of his abilities. If no common language is shared, the character can communicate only basic commands, such as "Come here," "Go there," "Fight," and "Stand still." the character knows what the subject is experiencing, but the character does not receive direct sensory input from him.
Obviously self-destructive orders are not carried out. Once control is established, the range at which it can be exercised is unlimited, as long as the character and the subject are on the same plane. The character need not see the subject to control it.
For obvious reasons, (I would think), it makes sense that to prevent abuse of the power/spell, one cannot make a dominated PC/NPC reveal plot-specific/sensitive information or give up an item they possess. I would even go so far as to say that if the player doesn't wish for their character to reveal a piece of (non-plot) information about their character that they feel uncomfortable revealing, there should be some courtesy given in that regard, as well.
However, I think there should be some clarification about what the extent is to which a dominated PC/NPC will go before their safety is "endangered". In the Avlis Wiki, it says that "obviously self-destructive orders are not carried out". They go into more specification as to what this means in the description of Dominate Animal, (which I also put because there are also animal NPCs to consider):
Avlis Wiki wrote:
The caster can enchant an animal and direct it with simple commands such as "Attack," "Run," and "Fetch." Suicidal or self-destructive commands (including an order to attack a creature two or more size categories larger than the dominated animal) are simply ignored.
Dominate animal establishes a mental link between the character and the subject animal. The animal can be directed by silent mental command as long as it remains in range. The character need not see the animal to control it. The character does not receive direct sensory input from the animal, but the character knows what it is experiencing. Because the character is directing the animal with the character's own intelligence, it may be able to undertake actions normally beyond its own comprehension, such as manipulating objects with its paws and mouth. The character need not concentrate exclusively on controlling the animal unless the character is trying to direct it to do something it normally couldn’t do.
It seems that it isn't entirely unfair to make a dominated PC/NPC attack someone/something, so long as it isn't obviously self-destructive for that PC/NPC to do so.
One last thought: what about making a PC/NPC do something that is against their nature? I realize that one must pass a Will save in the first place before becoming dominated, but one still maintains some semblance of self while under the spell/power. If I dominated Tris and told him to slaughter the children in the orphanage, shouldn't he be allowed a second Will save (adjusted or not) to resist such a command? Or is this just a courtesy one should offer when engaging in the use of Domination, since it's all about enhancing the roleplaying experience and not screwing over a fellow player/DM-controlled NPC?