How to pronounce "efficëint"
From what i heard, the "c" in this letter pronounce something like /ch/ or /g/. As far as i know, the letter c in Dutch is only used in foreign language, normally it only pronounces /s/ or /k/. Did you hear correctly? Or do you have miss something?
The combination of the letters CIEN is pronounced in some words as SJEN. This happens only when CIEN is pronounced as two syllables.
Keep in mind that elektricien and opticien are pronounced differently than coëfficiënt and financiën. The former are fairly recent loanwords from French, so the -cien part is pronounced similar (identical?) to the way it's pronounced in French.
Coëfficiënt and financiën simply have standard Dutch pronunciation, the accents are to incidate that the ie part is not to be pronounced as a single vowel, but rather as a separate i and e (the same goes for oë o and e, not oe).
An example of efficiënt: https://forvo.com/search/efficient/nl/ (keep in mind that ciënt pronounced by a native speaker, often blurs to sjent, especially when spoken normally/quickly like in the example).