Does the target know scrying? When the spell ends, the creature knows it was charmed by you. In the absence of similar text, the target of Scrying does not know, by default, that they are the target of this spell. This is spelled out in the PHB section on Targets (p. 204, bold added):
What is the DC for scrying? A scrying eye is an item that allows a person to cast the scrying spell for up to ten minutes with a spell save DC of 15. It can only be used once per day, and then cannot be used again until the next dawn.
Do Scrying modifiers stack 5e? The scrying modifiers stack. Modifiers are different from bonuses, but also, it’s only bonuses of the same type that do not stack. Bonuses of different types, or untyped bonuses, stack, and the scrying modifiers are all untyped.
Can Blindsight see Scrying? The exact wording of Scrying is: On a failed save, the spell creates an invisible sensor within 10 feet of the target. You can see and hear through the sensor as if you were there. The sensor moves with the target, remaining within 10 feet of it for the duration.