electrostatics - Is it correct to say that electro-static potential of a charge is the energy of a motionless charge?

Is it correct to say that electro-static potential of a charge is the energy of a motionless charge?

_{I ask this to better understand this (great) answer;}

Answer

Is it correct to say that electro-static potential of a charge is the energy of a motionless charge?

If you are speaking about electrostatic potential energy,
Than a motionless charge, as well as a charge in motion, can have an electrostatic potential energy. Just like a motionless mass $m$ a height $h$ above and close enough to the surface of the earth that the acceleration due to gravity is constant, can have a gravitational potential energy of $mgh$.

If you are speaking about electrostatic potential,
Than that would be the electrostatic potential energy per unit charge, or in the case of gravitational potential energy, the gravitational potential energy per unit mass.

That said,
The reason why your linked session says "practically we can't measure the (electrostatic potential) energy of a charge" is that they are talking about an absolute value for this energy. In general there is no absolute potential energy of a charge unless an absolute value of potential energy (or potential) is arbitrarily assigned a value of zero to some position.

Consider the gravitational potential energy analogy. If a motionless mass $m$ is a height $h$ above the floor in a room, it is said to have gravitational potential energy of $mgh$ with respect to the floor of the room. But if the floor of the room is also a height $h$ above the ground outside the building containing the room, the mass has a gravitational potential energy with respect to the ground outside of $2mgh$. If there is a surface of table in the room a height $1/2$ h from the floor, the mass has a gravitational potential energy of $(1/2)(mgh)$ with respect to the surface of the table and the floor of the room.

I think you get the idea.

Hope this helps.