if the bike is painted, not clearcoat over carbon, and if the paint is a 'lighter' shade, then you are just looking for micro-cracks, or a series of tiny cracks. Harder to see on clearcoat or dark colors. The places to check are bottom bracket and especially every other location where 'tubes' join. Most times it IS just a paint crack and not any issue, but that's the reason for a pic.
Don't be afraid to turn the bike upside down, the worst to be seen is on the bottom. Best to have someone (patient) stand the bike upright on rear tire while holding handlebars, so you can readily check the bottomside thoroughly.