can it be my boss in part time job ?
A 30 seconds search on CFAi website :
When selecting your references, please note that they are required to comment on your work experience and professional character. Select individuals who can describe and attest to your responsibilities in the investment decision-making process (as defined by our work experience guidelines). You will send instructions to your references as part of your application.
pretty self-explanatory I would say
source: https://www.cfainstitute.org/community/membership/process/Pages/professional_references.aspx