The Scrying spell states (emphasis mine):
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. A creature that can see invisible objects sees the sensor as a luminous orb about the size of your fist.
Notably, this is all that the Scrying spell says about the sensor.
The Locate Object spell states (emphasis mine):
The spell can locate a specific object known to you, as long as you have seen it up close – within 30 feet – at least once. Alternatively, the spell can locate the nearest object of a particular kind, such as a certain kind of apparel, jewelry, furniture, tool, or weapon.
If my character has both the Locate Object and the Scrying spells (and thus knows what a Scrying sensor is), can they use the Locate Object spell to find a Scrying sensor?
This question asks what can be done with a Scrying sensor, and its top answer is interesting but largely extrapolates from the Clairvoyance spell. In this case, I would like to ignore the extrapolation, however, and assume that the Clairvoyance spell is a different case from the Scrying spell.
This question and its answers are a good start for deciding what can be targeted by this spell, but they do not clearly answer the case where the object's kind is something like "spell effect".
Best Answer
The sensor is not an object
What is confusing here is that the Scrying spells says
However that does not say the sensor is an object. Being able to see invisible objects does not mean that everything invisible that you can see also is an object.
Object is a defined game term,
Objects are physical in nature, not spell effects. The DMG on p 246f has a list to assign AC and hp to them based on material and size. Listed there are cloth, paper, rope, crystal, glass, ice, wood, bone, stone, iron, steel, mithral, adamantine. Also, all the size examples are physical objects: a bottle, lock, chest, lute, barrel, chandelier, cart, window. "force" or "magical effect" is not on the list.
So the sensor as a magical effect has no AC or hp, and is not an object.
Because it is not an object, it also cannot be the target of Locate Object.