If the conditions are better, you can also go to GIA, a gemological institute in the United States, or HRD in Belgium for further study, but there are requirements for funds and academic qualifications and international qualifications.
If you just want to know this knowledge by yourself, not in theory, then read some books about diamonds, or look for some information on the Internet, but the most important thing is practice, that is, you can see more real diamonds, compare and observe various grades and types of diamonds, and really understand and use them.
If you can, you should also consult senior people in this field, but you should put aside the business aspects. After all, businesses are not particularly objective.