The range of Scrying is "self", so the caster targets him/herself first
The spellcasting rules says that the target must be withing range:
The target of a spell must be within the spell's range
However, range of Scrying is "self", so initially the caster is targeting self, not the creature he/she is scrying:
Scrying
5th-leveI divination
Casting Time: 10 minutes
Range: Self
You can see and hear a particular creature you choose that is on the same plane of existence as you...
After you target self and cast the spell, the spell effect gives you an ability to "see and hear a particular creature you choose". The "target" mentioned afterwards means this "particular creature" and does not obey the general rule for targeting — it has its own specific rules based on the target familiarity.
Furthermore, RAW a clear path to the target is required when the spell affects the target:
A typical spell requires you to pick one or more targets to be affected by the spell's magic. A spell's description tells you whether the spell targets creatures, objects, or a point of origin for an area of effect
The Scrying spell does not affect the target, it "creates a sensor":
the spell creates an invisible sensor within 10 feet of the target
I guess it's another reason why "A Clear Path to the Target" might not be applied.
Third reason — the common sense. There is little or no sense in a scrying spell, that requires you to see the person you're scrying in order to work. If a DM adjudicate Scrying this way, nobody won't use this spell in their games.
Final verdict: No, the Scrying spell does not require you to have a clear path to the target.
The creature does not know.
According to the spell description and the specific scope of this question, creature knowledge is dependent upon the Charmed condition.
From the Charm Person spell, with emphasis placed where the text calls for the Charmed condition:
The charmed creature regards you as a friendly acquaintance. When
the spell ends, the creature knows it was charmed by you.
The spell description says that for you to know that you were charmed, you have to have experienced the Charmed condition. This is reinforced by the word was, which shows that the condition must have existed in the past. Not that the condition almost existed (you made your save), but that it actually did.
There are obviously many other ways that the target of a Charm Person spell who made a successful save could know that a spell was attempted. "Is Charm Person obvious?" addresses these cases. I am only answering the specific question of whether succeeding on a save alone lets a target become aware that a Charm was attempted.
Best Answer
Not by default
Some spells specify that their target knows they that they are being magically influenced. For example, the target of Charm Person (PHB, p. 221):
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):
A tweet from Jeremy Crawford further clarifies that it is not automatically evident what is, and isn't, the target of a spell.
Since the spell, if cast far away from the target, has no visible effects before the saving throw has been made (or afterwards, if the target cannot see invisible things), most creatures will not know you are casting this spell on them.
Of course, there are plenty of ways that a person could know that you are casting the spell. They could see you casting it while holding a personal item of theirs, or you could have told them ahead of time that you will be casting this spell at a specific time of day. But by default, a target would be unaware.