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what is voltage at electrical level

Voltage is not an absolute. It is ALWAYS the difference on the electrical TENSION between two points. By extension, if only one point is given, such as the "voltage at " some point, that is generally that the second point, not given, is the "mass", which can the ground for a domestic network of distribution of electricity, the "casing" of a hand hell device, such as a cell phone, or the background for an antenna. Sometimes, using an expression such as "the voltage at" may mean the voltage drop at a resistor or a diode. For a BJT, "the voltage at the base" is generally the difference of tension between the base and the emitter.

You need the context to be sure of which TWO points are involved.

That being said, the voltage at a point of the ground, is zero, since the tension between a point and itself, is zero. Well, in general. You may have, as transient, a "ground loop" which would invalidate that last simplification: an influx of electrons need time to become uniform, even in a metal, so you can, for a short moment, a net current between two points both at the mass. And that is one of the reason why a lightning strike may damage your equipments, since for a short time, the "ground" is greatly disturbed, reversing the electrical tension and killing eventually the electronic.

But if some teacher is asking that question, just answer: 0. That is the "expected" answer.