How would a person check volts to ground on a 4 hole dryer receptacle?

On the dryer receptacle the U shaped pin is the ground, designated with the letter G if looking from the back side. Apply your tester to the outside left slot, designated with the letter Y if looking from the back side, and the U ground slot and you should read 120 (nominal) volts. Now apply your tester to the outside right slot, designated with the letter X if looking from the back side, and the U ground slot and you should read 120 (nominal) volts to ground. You should get the same readings, as above, if you test to the bottom neutral slot, designated with the letter W if looking from the back side. If you test from outside slot to outside slot you will get a reading of 240 (nominal) volts.

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As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.

Before you do any work yourself,
on electrical circuits, equipment or appliances,
always use a test meter to ensure the circuit is, in fact, de-energized.

IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB
SAFELY AND COMPETENTLY
REFER THIS WORK TO QUALIFIED PROFESSIONALS.