Ap

I don't have any resources for psychometry or Psychoscopy as i don't spend time reading books or looking on the internet related to these things, but what i can tell you is that it's all related to our knowing mind. Dr Joe Dispenza calls a part of it The Quantum world, you'd get many insights about that mind if you checkout his studies and books, i didn't get time to check those out, so I'm not able to give you specific details about that from his studies.

There were peoples here in this group who tried to read the energy of some others from their texts and what they were saying, at that time they where doing Psychoscopy on an energetic level. Psychometry, energy reading, these all are just Labels for the process of accessing different informations(which is also energy) about someone or something through different nonphysical ways, which is part of our claircognizance, i.e knowing mind. Those abilities are just an after affect when parts of our consciousness merges with the knowing mind through different practices.

A spiritual answer for your question would be that, we are the source/resource for these abilities. It's part of our true nature and state of being.

Few things i have to say is that,

- Have that genuine curiosity or goal to discover these things, instead of being wishy-washy (The answers you get depends on the bandwidth of the questions and seeking you have in your heart).

- whatever spiritual or mind related methods/practices you're doing (like AP, LD, Meditation, Energy works, healing, etc), also become aware of it's core mechanisms/workings, how all these things works, instead of just doing it. In that way, you can eventually discover what you want. 

- Know that all these things are not outside but inside, right on our finger tips. There's nothing to find...in a way. It's all are things that already exists which we just need to become Aware. We are already claircognizant when it comes to spiritual knowledge.

Some other little yet necessary tips,

- THINK WITHOUT WORDS, in that way, the awareness is more connected to the knowing mind. 

- know/accept that anything is possible, so it'll break the limitations of our imagination.

- Get rid of the labels of the things related to our internal worlds like "Thoughts", "Thinking", "Ideas", "beleifs" and become aware of how these things like Thinking, believing, etc actually works without these labes. Labels are related to the word based thinking mind. Have that desire to know how these things actually works. Never try to make a word based definition or theory of these things, instead become aware of how it works in practicality. Use these things to trace the mechanisms of other parts of our being.

- Don't accept or reject whatever you discover, right away. Have an open mind that considers all perspectives instead of accepting or rejecting it right away.

- Use AP, LD, energy works, other practises to realize how everything works.

You can even figure out some important things from the few tips i said above. First it needs to be put into practicality. Same way, you can discover things/workings behind others studies, teachings, books, tutorials.