Licensed, Diploma, Certified adhd coach… Accredited training – what’s what?

A license is issued to someone who then becomes licensed.
Licensing is allowing someone to use something, e.g. a player’s license, a material, a patent or the like. Someone is a licensee and someone else is a licensor.
A question to ask in this context is who is the licensor and what rights are included in the license.

A diploma is a type of proof of e.g. completed training, or a special achievement. A diploma can be issued by any institutions or organisations for any purpose or achievement.
A question to ask in this context is: who issues the diploma / writes the diploma, and on what grounds.

To provide someone with power of attorney. e.g. an education that lives up to official expectations regarding quality, content and learning.In education, it is, for example, a matter of an institution of higher education accrediting an program which, after examination, can give awards in higher education credits.
An officially recognised and specialised organisation can also be the credentialing body for the accreditation.

A question to ask in this context is who is the credentialing body for the education/training program and on what grounds are they accredited.

The person who is certified is officially recognised for meeting set requirements of knowledge and academic excellence after passing the examination of an accredited education. To certify is to provide someone with a certificate as proof of eligibility and specialised competence.
Two questions to ask in this context are:
Which is the credentialing body?
What are the requirements to become certified?