How we can enhance our theoretical knowledge about printing technology.?
Interesting question and one that is full of traps.
There are many forms of knowledge. There is knowledge that is based on experience and there is knowledge based on theory and there is knowledge based on a combination of both. This is related to the difference between science and technology. They are not the same thing.
There is also knowledge that is based on invalid theoretical view points which if believed, can hold back innovation for decades.
The printing industry has a lot of practical knowledge based on experience which can be very helpful for users. The knowledge needed for innovation needs to be mostly theoretical if it is to make significant improvements. One could make improvements with trial and error methods but this is a very costly approach. One could make improvements by applying known engineering solutions (technology) to existing problems, which does help but it does not tend to solve the fundamental problem but only copes with it.
The application of a technology does not mean that the fundamental science of the problem is known. Closed loop colour control is an example of a technology being applied by engineers that don't understand the fundamental causes of colour variation.
If your question really does relate to theoretical knowledge as opposed to general knowledge about printing methods and technology, then there is a serious problem. The printing industry does not have a good source of valid theoretical knowledge. There are associations such as TAGA and Iarigai, plus the graphic arts related institutions but all of those groups are mostly interested in technology and have had a very poor track record of actually understanding fundamental problems and solving them. They can't explain the simple problems and I have a strong belief that they don't really understand the more difficult problems even though they try to make their work look scientific. Their work usually lacks predictability.
People in these groups might think they are doing science but if asked to actually make an improvement to the process based on their work, I doubt they would be able to do much. The only area that I see as being able to develop new innovations are the engineers designing new ink jet technologies, etc., which is based on more valid theoretical knowledge that has been used to advance these technologies.
So if in fact you really do want theoretical knowledge then you have a problem. My guess is that about half the theoretical type of literature in the printing industry is wrong or basically useless. You already have to know what is true to know which half is the good stuff.
The printing industry is a technology driven industry and not a science driven industry even if people think there is a lot of science supporting it.
Good luck in you efforts to increase your knowledge.