For a Traction Separation interface behaviour, there are three property values to be set: E/Knn, G1/Kss & G2/Ktt. I am looking for the method to determine/calculate the values.
The correct answer to this question depends on the definition of the constitutive thickness of you cohesive section.
If you are defining the constituive thickness in terms of the “true” thickness of you interface, you should use E,G1 and G2 equal to the elastic moduli of your interface material.
When the constitutive thickness of the cohesive layer is “artificially” set to 1.0, ideally you should specify Knn/Ktt/Kss as the material stiffnesses calculated with the true thickness of the cohesive layer.
Same considerations hold for the definition of the density of your material with a traction separation law.
For more detailed info see the (Section 32.5.6 Defining the constitutive response of cohesive elements using a traction-separation description) in Abaqus Analysis User’s Guide.