You can model cohesive zone either using element based cohesive behavior (cohesive element with finite thickness) or surface based cohesive model ( contact pairs with zero thickness). To assign material properties for element based cohesive model, you need to create the section and assign material properties and also select element type during meshing as cohesive element. In material edit box, you may select mechanical, elastic and from elastic there is an option for traction, then you may use this option to input your proprieties in case you are interested to use traction displacement model. For surface based, you create interaction as a contact between the surfaces you want to create the cohesive zone and then assign material properties of the contact using cohesive model (traction displacement approach).

Hope this helps.