what engine oil do i need for a peugot 306 20 i cabriolet 1997

only two ways. jak up car and drain from petcock. or if your milage is a neer 3000 sinse that change l would suggest just oil change sinse you will already be under their.
if you lossen the filter to drain the oil the seal around it wont hold when retighted you will end up with oil all around your engine bay.
good luck

Use 10/40 semi synthetic (good quality stuff), we use this in the vast majority of the cars we service at work.