Skeptical means having a doubtful or questioning attitude, often towards new ideas or information. It is an adjective that describes someone who approaches new claims with caution and requires evidence before believing them to be true.
He urged his colleagues, many of whom are among the most ardent remainers, to try to understand the concerns of voters sceptical about the European Union. (theguardian.com)
I'm also a bit of sceptical of what details will do in practice. (matt.garrish.ca)
I'm still very sceptical about Wenger getting a DM. (justarsenal.com)