The Klingon word for instincts is Duj, and it is grammatically correct to treat it as singular (a bundle or collection of instincts) or plural (individual instincts). (TKW, p. 27)Marc Okrand repeated this in his answer to a request for a singular form:
Duj can be considered singular ("bundle of instincts") or plural ("individual instincts"), so Maltz assumed that this request is for "instinct" in the sense of (innate) talent, facility, aptitude, or skill in a particular area (as opposed to intuition or sixth sense or "gut" or whatever). That word for this is re'lIng. (qepHom 2021)