How to get the Parent’s parent directory in Powershell?

Version for a directory

get-item is your friendly helping hand here.

(get-item $scriptPath ).parent.parent

If you Want the string only

(get-item $scriptPath ).parent.parent.FullName

Version for a file

If $scriptPath points to a file then you have to call Directory property on it first, so the call would look like this

(get-item $scriptPath).Directory.Parent.Parent.FullName

Remarks
This will only work if $scriptPath exists. Otherwise you have to use Split-Path cmdlet.