Measuring high voltage low current using a resistor and measuring the amps
Meter specs tend tend to use 250v or 500 V rated parts. Exceeding these ratings by some margin may result is catastrophic failure to other parts when an arc bypasses the part.

There are 10:1 to 1000:1 probes rated to higher specs  which must be observe/chosen.

Using high voltage rated resistors you can make a voltage R divider for DC and for AC use high voltage rated capacitors to make a C divider.
 (not to scale)  $1 rated for 6.1kV







simulate this circuit &ndash; Schematic created using CircuitLab