"Creationism" can span a variety of beliefs and/or theories. There is young Earth creationism versus the broader concept that life on Earth was created by God or an intelligent being. There is creation of human beings, creation of all living things on Earth, creation of the Earth itself and creation of the universe.
I want to give a specific senerio of how creation could be proven or disproven.
If there is nothing unique about intelligent life on Earth, (whether we were created or came into being spontaneously) it is entirely possible that another civilization observed the creation or spontaneous developement of human beings.
Certainly for those who argue for abiogensis of life on Earth and subsequent evolution, it is reasonable to consider that similar events occurred elsewhere and that other intelligent beings exist or have existed. Just as scientists on Earth are extremely interested in searching for life on Mars and exoplanets, so would other intelligent beings be. These beings could have observed our creation or abogensisabiogensis and evolution and recorded it and in principle such records could be transferred to us or discovered by us.