The unit J Pa^-1 is equivalent to

JPa^-1; Unit of work is Joule and unit of pressure is Pascal. 

$\text{ Dimension of Joule i.e. work }=\mathrm{F}\times \mathrm{L}={\mathrm{MLT}}^{-2}\times \mathrm{L}$

$\begin{array}{l}=\left[{\mathrm{ML}}^2{\mathrm{T}}^{-2}\right]\\ \frac{1}{\mathrm{Pa}}=\frac{1}{\text{ Pressure }}=\frac{1}{\frac{\mathrm{F}}{\mathrm{A}}}=\frac{1\times \mathrm{A}}{\mathrm{F}}=\left[{\mathrm{ML}}^{-1}{\mathrm{T}}^{-2}\right]\end{array}$

$\text{ So, }\left. J {\mathrm{Pa}}^{-1}=\frac{\left[{\mathrm{ML}}^2{\mathrm{T}}^{-2}\right]}{{\mathrm{ML}}^{-1}{\mathrm{T}}^{-2}}=\left[{\mathrm{L}}^2\times \mathrm{L}\right] = L^3 \right]$ = volume in S I units .