Whosever microphone is on, please turn it off.
Whoever's microphone is on, please turn it off
Whosoever left their microphone on, please turn it off
genitive (N/Adj) — in grammar the possessive form See Genitive Noun Forms.
interrogative (N/Adg) – in grammar, a word used to form a question (e.g., who, what, where, why, when, how). See Interrogative Pronouns.
lose favor (idiom) – become less popular or less preferred
- "whosever." Mirriam-Webster. merriam-webster.com/dictionary/whosever.
- "who(so)ever, whom(so)ever, whoso(ever), whomso(ever), C. Possessives." Garner's Modern American Usage. By Bryan A. Garner, 3rd ed., Oxford UP, 2009.