Catalysts find use in many scientific and engineering applications. One of the recurring themes in this context is the quest for the design of suitable catalysts with improved performance. A prerequisite for the rational design is the identification of the nature of the catalytic site(s). XPS is a widely used experimental technique for this purpose. However, the unique identification of structural motifs from XPS observations remains challenging. Firstprinciples computations can provide the missing link by predicting corelevel shifts for candidate structural motifs of the catalytic sites. Here we focus on carbon supported TMNx (TM=Fe, Co) electrocatalysts, a class of ORR electrocatalysts that continues to attract significant attention for applications in fuel cells. Using densityfunctionaltheory (DFT) we predict the Fe2p and N1s core level shifts for carbon embedded candidate TMNx (TM=Fe, Co; x=14) motifs. In particular we will discuss single versus multielectron excitations, the effect of electronic relaxation in the final state approximation and provide a comparison our experimental observations.