The Collaborative International Dictionary of English v.0.48:

Enquirer \En*quir"er\, n.
   See Inquirer.
   [1913 Webster]

WordNet (r) 3.0 (2006):

enquirer
    n 1: someone who asks a question [syn: inquirer, enquirer,
         questioner, querier, asker]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "enquirer":
   ask, ask a question, ask about, ask questions, be curious,
   bring into question, burn with curiosity, demand, dig around for,
   dig up, gape, gawk, inquire, inquire of, interpellate, interrogate,
   make inquiry, nose around for, nose out, peer, propose a question,
   propound a question, put queries, query, question, quiz,
   require an answer, rubber, rubberneck, seek, stare, want to know