I have something that is over ten years old can they still use it against me

There is a six year statute of limitations on claims for written contracts. https://app.leg.wa.gov/RCW/default.aspx?cite=4.16.040

Is my son's prank involving jumping out onto people and screaming at them a violation of the law?

The definition of "assault" includes "putting another in apprehension of harm whether or not the actor intends to inflict or is incapable of...

Do I have an actual personal injury case?

See RCW 7.72. https://app.leg.wa.gov/RCW/default.aspx?cite=7.72

Do any of the following get settled on the property side of a claim?

Property damage coverage usually only covers property damage.

Can my employer require me to waive my rights, in order to take mandatory training they are providing?

It looks like boilerplate language. See the following: 62A.2-302 Unconscionable contract or clause. 62A.2-314 Implied warranty:...

If a sign from a drive-thru restaurant falls and damages my car, who would be responsible? The sign company or restaurant?

It appears from your statement that the sign company (or their insurance company) should probably pay for your damages.

Can testing my handbreak while at slow speeds with no one or cars around land me in jail?

"Reckless driving" is defined as driving any vehicle in willful or wanton disregard for the safety of persons or property...." ...

Maybe the officer saw you weren't wearing your seatbelt.

Breaching a lease?

Check the specific terms of your lease agreement. Call the Tenants Union. https://tenantsunion.org/en

How do I find out whether a lawyer or his law firm is legit?

Check with the PA and DC bars. Admission to practice in federal courts is different from State courts. Nonetheless, as previously observed, State...