I bought a 400KV high voltage generator, it looks like tube, a pair of wires stick out from two holes at the top and bottom. Can I run any tests with a digital multimeter or any other device to see if it is working and it is safe to use?
Safety depends on many externalities. Those
HV generators look to have no safety features
(aside from primary:secondary isolation) and
as soon as you close the ground loop (with
wire, or meat) then it's all on practices more
than materials.