Can someone suggest a few solid reads for someone who is getting really into professional dog training?

I was following an online course but the institution has announced it will be shutting down activity, so I decided I will instead continue building my knowledge base through reading and resort to the vet that usually follows my dogs for advice. I’m also about to volunteer hours at dog shelters to prepare dogs for adoption and manage the individuals deemed “unruly”. These last ones are usually confined for life, with little to no interaction, as my country presently has a hard no kill policy on shelters.

One note: being a dog trainer in my country is not a profession, in the formal sense, like being a veterinarian, so anyone can call themselves a dog trainer and use whatever brutal or absurd methods to “train”.

The exception to this is being a recognized dog trainer for dangerous dogs and dogs of potentially dangerous breeds but there is not formal course I can take to achieve this. I simply have to train at least one animal that fills the requirements I previously mentioned, pay a fee, and wait to be called to be evaluated by a panel made of K9 squad members of our police and members of a government department that oversees animal welfare.

My personal objective is to get this certification, for personal validation.

Please, leave a few ideas and recommendations.

Thank you in advance.