How to access Default properties and custom properties using Groovy scripts.

The actual Groovy syntax will vary subtly depending on where the properties are coming from, The best way to retrieve the data when you're not sure of the syntax is to use the "Get Data" functionality accessed from the right click menu, see:

https://www.soapui.org/getting-started/point-and-click-testing.html#3-Point-and-Click-testing-in-Groovy-script

This will add the required Groovy code for you.

In what context? Default / Custom Properties of a request step or groovy step? Please clarify.

The SoapUI site gives a following guide on using properties within Groovy scripts:

https://www.soapui.org/scripting-properties/tips-tricks.html#1-Accessing-Properties--Settings-and-Names

It also helps to get familiar with the SoapUI object model:

https://www.soapui.org/scripting---properties/the-soapui-object-model.html

Karel