1-a quick method to find out the column volume?
"column volume" is a bit ambiguous. The bed volume (volume of resin in the column) is easy: V = 1/4 * (pi * dc^2 * L) where dc is the radius of the column (half the diameter) and L is the length. The "void volume" (Vm = the amount of mobile phase in the column) is a bit more complex. For silica-based materials commonly used in HPLC, that can be estimated as Vm ≈ 0.5 * (dc^2 * L), but that assumes that the pore volume is around 30 - 35% of the packing particle volume, which is not necessarily true for other types of packings. When all is said and done, if you want an accurate value, you have to measure it by injecting a non-retained solute to find the dead time.
2-if in this type of chromatography it is more important to know the column volume or the void volume?
They serve different purposes. If you want to know how much resin it will take to fill your column, then the bed volume is more important. If you want to characterize elution time, then you need the void volume.