I said I was interested in optometry and I'd like to shadow him. At the end of the first day, I asked if I could come again next week same time and he said that was fine but he wanted me to call the office and clear it with them first which was a little annoying since I didn't get to ask him directly ever.
Towards the end, just casually and politely ask if you could come in regularly and set up a time that is convenient for both of you. They know what you're going through since they had a similar experience when shadowing.