Spell Ruling: Geas in Toril in the Age of Enialis | World Anvil

Spell Ruling: Geas

Geas can only be a single command.
"You can issue any command you choose, short of an activity that would result in certain death. Should you issue a suicidal command, the spell ends."  
Note: You cannot issue the command to "Do whatever I say" or "Be my slave."
Note: Compound commands joined by "And" may be ignored by the creature.  

Unless the spell specifically states that the creature can "choose to fail," there is no way to force the creature to fail a saving throw even if it is under a spell that gives the caster total control of it.  Therefore, even if you have Dominated the creature you can't force it to fail the save to force it to be under Geas.

A creature cannot be under 2 Gaes spells at the same time.  The latter cast spell will take precedence.