We explore the multi-faceted important features of turbulence (e.g., anisotropy, dispersion, diffusion) in the three-dimensional (3D) wavenumber domain ($k_parallel$, $k_{perp,1}$, $k_{perp,2}$), by employing the k-filtering technique to the high-quality measurements of fields and particles from the MMS multi-spacecraft constellation. We compute the 3D power spectral densities (PSDs) of magnetic and electric fluctuations (marked as $rm{PSD}(delta mathbf{B}(mathbf{k}))$ and $rm{PSD}(delta mathbf{E}_{langlemathbf{v}_mathrm{i}rangle}(mathbf{k}))$), both of which show a prominent spectral anisotropy in the sub-ion range. We give the first 3D image of the bifurcation between power spectra of the electric and magnetic fluctuations, by calculating the ratio between $rm{PSD}(delta mathbf{E}_{ langlemathbf{v}_mathrm{i}rangle}(mathbf{k}))$ and $rm{PSD}(delta mathbf{B}(mathbf{k}))$, the distribution of which is related to the non-linear dispersion relation. We also compute the ratio between electric spectra in different reference frames defined by the ion bulk velocity, that is $mathrm{PSD}(delta{mathbf{E}_{mathrm{local} mathbf{v}_mathrm{i}}})/mathrm{PSD}(delta{mathbf{E}_{ langlemathbf{v}_mathrm{i}rangle}})$, to visualize the turbulence ion diffusion region (T-IDR) in wavenumber space. The T-IDR has an anisotropy and a preferential direction of wavevectors, which is generally consistent with the plasma wave theory prediction based on the dominance of kinetic Alfven waves (KAW). This work manifests the worth of the k-filtering technique in diagnosing turbulence comprehensively, especially when the electric field is involved.
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