Precise knowledge of the local density of optical states (LDOS) is fundamental to understanding nanophotonic systems and devices. Complete LDOS mapping requires resolution in energy, momentum, and space, and hence a versatile measurement approach capable of providing simultaneous access to the LDOS components is highly desirable. Here, we explore a modality of cathodoluminescence spectroscopy able to resolve, in single acquisitions, the dispersion in energy and momentum of the radiative LDOS. We perform measurements on a titanium nitride diffraction grating, bulk molybdenum disulfide, and silicon to demonstrate that the technique can probe and disentangle the dispersion of coherent and incoherent cathodoluminescence signals. The approach presented raises cathodoluminescence spectroscopy to a versatile tool for subwavelength design and optimization of nanophotonic devices in the reciprocal space.