Just measuring it using the measure tool? You can select the vertices (corner points) or the edges of the diagonal. That should give you measurements in X, Y, Z and diagonal direction. If the measure tool doesn't give these answers, you might have to fiddle with the settings at the top of the tool.
Just pick the two points (using ctrl selection) and get the desired value here
OR use measure tool as Peter has suggested. You can find it under Tools > Evaluate > Measure OR M key OR Evaluate toolbar
In addition, please go through inbuilt SOLIDWORKS tutorials to help you understand the basic tool/features. You can use the SW help and search function also
Just pick the two points (using ctrl selection) and get the desired value here
OR use measure tool as Peter has suggested. You can find it under Tools > Evaluate > Measure OR M key OR Evaluate toolbar
In addition, please go through inbuilt SOLIDWORKS tutorials to help you understand the basic tool/features. You can use the SW help and search function also