JAM is for M.Sc and not MCA. However you are asking about MCA so I must tell you that UCEED is for undergraduation and so a class 12 student of commerce can apply for this as it is for admissions to B.Des. If you are a graduate then you must appear for CEED and the eligibility for that is

Candidates must have passed a degree / diploma / post graduate degree programme of 4 years or 3+2 years (after 10+2 level), or must be appearing for the final examination of such a program by July 2018, or must have passed the GD Arts diploma programme (10+5 level)