Voltage on one lead of panel

Voltage measurements are always done with two leads to the meter. DMM (digital multimeters) are great devices, but they have one possible drawback. They draw very little current from whatever they are measuring (1-10 million Ohms resistance is common). That means any little leakage current or stored energy (capacitance, even just the stray capacitance of solar panel to the "world"). Add a little bit of static charge--You can "charge up" the solar panel and read the voltage with the DMM (you are seeing the meter slowly discharge the capacitance of the panel).

For debugging, a test load (like a light bulb) across your test points will either light the lamp (there is enough current to do this) or it will discharge the stray capacitance. You can even get DMMs that have a "low resistance" mode (it appears this meter uses a 3,000 Ohm resistor to discharge):

https://www.amazon.com/gp/product/B019CY4FB4/ref=ox_sc_saved_title_4?smid=ATVPDKIKX0DER

The above meter is also a DC/AC Current Clamp type meter... Current clamps are very easy (and safe) for debugging your systems.

Just to give you an idea, 5 mAmps (0.005 Amperes) or less through the human body is relatively safe (you can still feel the shock). Above that level, and you start to run the risk of stopping your heart (if the current goes through a leg and arm, for example).

Voltage wise, it depends on conditions (wet skin, salty water/sweat), Above ~12 volts can give you a shock. Above ~24 to 60 volts is a risk. Above 60 volts is "unsafe". But you have to have the current also (> 5 mAmps). For example, you can get shocked by walking across a carpet and get a multi thousand volt shock. But it will not kill you (not enough current/time).

So--Your question, can you get a shock (or get hurt) from touching one lead of solar panel. As always, the answer is "complicated"...

A single solar panel on the floor, no problem. A large solar array on a second story roof, there is a lot of capacitance and possible charging from the earth's natural magnetic   electric field. In clear air, is (very roughly) 100 volts/meter... Get on a second story roof system, ~6 meters is ~600 volts of static charge. Add a thunderstorm in the area, and you can get many thousands of volts per meter of static charge.

https://en.wikipedia.org/wiki/Atmospheric_electricity

While you probably will not get killed... The surprise of an electric shock could knock somebody off a ladder if they are not careful (why electricians always use fiberglass ladders vs aluminum).

Once the solar panels are connected, there is usually some sort of ground reference somewhere... But you are still left with Voc/Vmp --- With enough current from the sun to still hurt you. Put two or more Voc~20 volt panel in series, and you now have enough voltage/current to actually be lethal (over 60 volts, over 5 mAmps).

-Bill