You are asking a very good question - similar to ‘how do you measure the qualities of the drop of water in the middle of a flowing river?’
More seriously - when you see ‘highly spiritual’ people (especially psychics and mediums) on social media websites using crude language, making aggressive statements, being judgmental of everyone and losing their dignity in public every day, you do wonder.
I can only give you my take on this based on my personal experience. Spirituality cannot necessarily be measured, but the opposite of being spiritual is very visible and measurable, as indicated in the examples above.
If you want to know whether a person is enlightened and spiritual, I would say look at what that person does and says consistently, and at the effect that person has on those around them. A truly spiritual person inspires others with everything they say and do without being holier than thou, because spirituality comes from having life experiences, gaining wisdom from those experiences and becoming whole.
In my view people who run courses to ‘change DNA’, ‘increase vibrations’ and other weird and wonderful things, do all of those in a single dimension, without understanding what they are dealing with.Spirituality is neither about positive thinking (which I think is a form of depression) nor about the Buddhist view of life being about suffering, because life is balanced, i.e. filled with experiences that we interpret as positive or negative ourselves.
There are a number of books that I found quite useful in my own journey to understand what spirituality is about. Don't be put off by the titles - these books are really informative.
Michael Talbot’s The Holographic Universe
The Field by Lynne McTaggart
A Beginner's Guide to Constructing the Universe by Michael S Schneider
The Men Who Stare at Goats by Jon Ronson
Punk Science - Inside the Mind of God by Dr Manjir Samanta-Laughton
Defining spirituality is an individual journey of awareness, and those books can only add to your journey. No course or book can replace your awareness.
Love and Light (that is the quantum Love where emotions turn into feelings which form the vibration of Light ;-) )