The crystal electric field (CEF) plays an essential role in defining the magnetic properties of 4f materials. It forces the charge density of 4f electrons and the related magnetic moment to be oriented along a certain direction in the crystal. The CEF and related magnetic properties were widely studied in the past with focus on bulk of 4f materials, while their surfaces have not received much attention. By the example of the antiferromagnetic material TbRh2Si2 and using first-principles calculations and classical 4f angle-resolved photoemission (PE) measurements, we show how the CEF and related magnetic properties, linked with the orientation of 4f moments, are modified at the surface region. Precisely, we studied the CEF characteristics in individual Tb layers for Tb- and Si-terminated surfaces of TbRh2Si2. We show how strongly the CEF changes near the surface and how dramatically it influences the orientation of the 4f moments relative to the bulk. The instructive message of our study is that a rather valuable information about the CEF-related phenomena can be derived from the temperature dependence of 4f PE spectra. The presented methodology including the theoretical approach can be further applied to many other layered and quasi-2D rare-earth-based materials for unveiling their surface magnetic properties.