I should probably clarify my question.
Since Discern Lies is a targeted effect, the caster would know if their target succeeded at their will-save (and the target would know if they successfully resisted).
However, if they attempted to cast discern lies on someone under the influence of Glibness (which is neither a targeted spell or a saving throw, it requires a caster level check to bypass) would they be aware they succeeded or failed at bypassing an effect?
And would the target be aware that Glibness worked or failed?
I haven't been able to find anything either way on caster-level checks (which are usually made to bypass spell-resistance, so in most contexts successful resistance is fairly obvious).