I want to cite some articles directly in Semantics, Volume 2 by de Gruyter (2011). I wonder if each article in it is a journal or conference paper that can be cited directly. Otherwise, I should cite the entire book of Semantics, Volume 2, right?
Semantics, vol. 2 is authored by John Lyons, and published by Cambridge University press. That single-authored work would be cited as such. The item you are presumably referring to is Semantics: An International Handbook of Natural Language Meaning, edited by von Heusinger, Maienborn & Portner and published as Handbooks of Linguistics and Communication Science 33.2 published by de Gruyter, contains 36 articles each of which has a separate author and title. If you want to refer to the entire collection, you cite Semantics: An International Handbook of Natural Language Meaning, edited by von Heusinger, Maienborn & Portner etc. Otherwise you cite the specific article that you are referring to.