Which type of fuel is gobar gas? 

Gobar gas is also known as biogas. Cow dung is used to make gobar gas. Once all of the moisture has been dried out of the cow dung, it can be let to dry fully. Burning the dry cow dung produces gobar gas. 

The fuel that is obtained directly from nature is referred to as primary fuel. Examples: coal, wood, etc. Secondary fuel is obtained from primary fuel. Examples: charcoal, coke, gasoline, hydrogen fuel.
Since gobar gas is obtained directly from nature(living organisms) it is a primary fuel.