A wide-field galaxy redshift survey allows one to probe galaxy clustering at largest spatial scales , which carries invaluable information on horizon-scale physics complementarily to the cosmic microwave background ( CMB ) . Assuming the planned survey consisting of z \sim 1 and z \sim 3 surveys with areas of 2000 and 300 deg ^ { 2 } , respectively , we study the prospects for probing dark energy clustering from the measured galaxy power spectrum , assuming the dynamical properties of dark energy are specified in terms of the equation of state and the effective sound speed c _ { e } in the context of an adiabatic cold dark matter dominated model . The dark energy clustering adds a power to the galaxy power spectrum amplitude at spatial scales greater than the sound horizon , and the enhancement is sensitive to redshift evolution of the net dark energy density , i.e . the equation of state . We find that the galaxy survey , when combined with CMB expected from the Planck satellite mission , can distinguish dark energy clustering from a smooth dark energy model such as the quintessence model ( c _ { e } = 1 ) , when c _ { e } \lower 2.15 pt \hbox { $ \buildrel < \over { \sim } $ } 0.04 ( 0.02 ) in the case of the constant equation of state w _ { 0 } = -0.9 ( -0.95 ) . An ultimate full-sky survey of z \sim 1 galaxies allows the detection when c _ { e } \lower 2.15 pt \hbox { $ \buildrel < \over { \sim } $ } 0.08 ( 0.04 ) for w _ { 0 } = 0.9 ( -0.95 ) . These forecasts show a compatible power with an all-sky CMB and galaxy cross-correlation that probes the integrated Sachs-Wolfe effect . We also investigate a degeneracy between the dark energy clustering and the non-relativistic neutrinos implied from the neutrino oscillation experiments , because the two effects both induce a scale-dependent modification in the galaxy power spectrum shape at largest spatial scales accessible from the galaxy survey . It is shown that a wider redshift coverage can efficiently separate the two effects by utilizing the different redshift dependences , where dark energy clustering is apparent only at low redshifts z \lower 2.15 pt \hbox { $ \buildrel < \over { \sim } $ } 1 .