I usually put any big or long lasting pro bono placements under work history/experience unless they have a section about volunteering!
Yes, you can include these either in employment or if you would prefer, put it in a volunteering section on a CV. Some people choose to put these things in extra curriculars too - it's one.of the grey areas where it could fit into different sections depending on the rest of your experiences and where you think works best
Danke!