Not exactly sure what you mean. I'm going to assume that you mean other courses in addition to your compulsory courses.
Dear Sir/Madam
I am enrolled/registered [use whatever status is best for you] on xxxxxxx course. [give more details like start date etc. that will help identify you - if you have a student number include it]
Can you tell me how many additional non-compulsory [better term might be 'optional' - but your university might use the term non-compulsory, so use the term that they use] courses I can undertake and how to apply for these, as I cannot see any 'apply' option on the Unisono portal.