The strongest assassin gets transferred to another world with his whole class is a Manga/Manhwa/Manhua in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

The strongest assassin gets transferred to another world with his whole class An ordinary high school student by day, an assassin living in the underworld by the night. A boy with two faces, Aragi Kai. His classmates hate him because of his anti-social character and weird aura. One day, Aragi and his classmates were suddenly transferred to another world. It is a world of swords and magic. A woman who calls herself Leonora appears before the confused students, and declares… “You are ‘Hero Candidates’ summoned here to defeat the Demon King. Please help us.” Leonora grants each of the students a unique ability: ‘Divine Protection’. While some powerful ‘Divine Protections’ are given like telekinesis and destructive blast, Aragi’s ‘Divine Protection’ is judgment. It is a skill that allows one to see the details of the target, but since he was always a loner in class, he gets mocked by them for having a skill that is useless in battle. However, he operates behind the scenes in the parallel world with his abilities as an assassin and his calm situational assessments…