No, unfortunately you can't pick your placements generally! Some unis let you swap with people on your course though as far as I'm aware, Mine doesn't though! I just got lucky :P
I do have an elective placement this summer though (i'm in 2nd year) so if you have something similar, then you could try and find a diabetes related placement! Or you can ask on wards to spend a day with certain people! I've spent days with physios and dieticians so I don't see why you couldn't ask to spend the day with a diabetes nurse
I learnt loads! I learnt about all of the different insulins, the tablets for diabetes, about the other meds that a lot of dibetic patients are on and why, diabetes control (things like improving control clinics, starting people on pumps etc) about the problems associated with diabetes and why they happen (they had nephropathy and neuropathy clinics). They had people on injections for weight loss, just everything really! I spent half my week in the clinic, then half the week visiting patients on the wards. You realise just how badly diabetes is managed on the wards.
So I saw everyone from the ages of 16! Oh and I went a clinic which was run by midwives too for pregnant women who develop diabetes!
To be honest, in first year I had a case study for physiology on diabetes and I got 78% for it and I now know I had half of it wrong!
Sorry I've written you an essay but I just loved it so much there!