  We study how sharp signatures of fractionalization emerge in nonlinear
spectroscopy experiments on spin liquids with separated energy scales. Our
model is that of dipolar-octupolar rare earth pyrochlore materials, prime
candidates for realising quantum spin ice. This family of three dimensional
quantum spin liquids exhibits fractionalization of spin degrees of freedom into
spinons charged under an emergent $U(1)$ gauge field. We show that the
technique of two dimensional coherent spectroscopy (2DCS) can identify clear
signatures of fractionalised spinon dynamics in dipolar-octupolar quantum spin
ices. However, at intermediate temperatures, spinon dynamics are heavily
constrained in the presence of an incoherent spin background, leading to a
broad 2DCS response. At lower temperatures, a sharp signal emerges as the
system enters a coherent spin liquid state. This lower temperature signal can
in turn distinguish between zero-flux and $\pi$-flux forms of quantum spin ice.
