This is false information, and easily found to be so. Just searching "blaschko lines uv light" gives several results saying it's not true, and that there is never a source for that information in the articles, videos etc. that say it. It should also be obvious it's not true just by most people's experience, seeing people under UV light, via everything from clubs, movies, art, etc. isn't rare at all, and you never see these lines.

Check anything you say before doing so, we are all bombarded with misinformation from malicious intent already, no need to pile onto that with misinformation from ignorance.