First recommendation, go visit your local library for the service and repair manuals for the 2008 Isuzu.

Location of sensors and how-to-replace = www.automd.com/How-To-Guides

If no library, or service / repair manuals - then utilize these resources:

www.pdfmanual4trucks.com/isuzu;
www.rockauto.com;
www.onlymanuals.com/isuzu/other_model;
to list only a few...

The crank position sensor - is located on the right side of the motor, in the transmission area. Actually in the bell housing.

The cam position sensor - is located on the inner rear section of the left hand head (left side of vehicle) under intake manifold