What "practical knowledge" should every civil engineer know which is not written in books? 

•     How to handle labours in site.

•     How to check the quality of materials just by seeing or using thumb rules.

•     How to apply or know how the theory is applied in site.

•     Handling and knowing how local instruments like plumb bob, spirit level are used in site.

•     How to calculate the materials required using thumb rule.( example for concrete roofing a 100sqft area the thumb rule is it carries 6 to 7 bags of 50kg cement is the thumb rule used in site)