If you decide to have someone help you identify habitual waste in the work you do, don’t fret over whether or not they can do the work you do.
If you’re a lawyer, they don’t have to be a lawyer. In fact, it would be best if they don’t do what you do because they won’t have preconceptions about what you should do.
Most wasteful practices come from religious beliefs that we hold about the right way to do things. Often times the right way is actually the hard way and not necessarily a better way.
Someone without industry or professional bias will see through the nonsense that you’re blind to.
If you’re still concerned, then get two people to observe you. Someone that does what you do and someone that doesn’t do what you do. Two perspectives might be better than one.