  As observational evidence increasingly consolidates the case for a
cosmological constant being the source of the Universe's accelerated expansion,
the question whether, and if so, how well, future experiments could detect
deviations from this standard scenario is raised with urgency. Assuming a dark
energy component different from a cosmological constant, the observable effects
in general include gravitational clustering described by the fluid's
(rest-frame) speed of sound. We employ 3d weak cosmic shear, a proposed method
to take advantage of the full three-dimensional information inherent to the
cosmic shear field, to explore the capability of future surveys to detect dark
energy clustering and the signature of an enhanced amplitude of the matter
power spectrum on large scales. For this purpose, we present adequate numerical
methods facilitating 3d weak cosmic shear calculations. We find that the
possible constraints heavily depend on the dark energy equation of state w. If
w is not very close to -1, constraining the squared sound speed within an order
of magnitude seems possible with a combination of Euclid and Planck data.
