As far as I understood, you created a material using Workbench "Engineering Data" module and want to use that material in ANSYS APDL commands (in APDl GUI).
If this is the case, I get to say that we don't have a command that make APDL to use material defined in workbench.
Because as Zhengwei Fan explained, you can define material property for each of the components in the model using material ID and assign whatever properties you want using APDL commands. Therefore, there is no point for getting access to Workbench database.
However, if you define a material in Workbench using "Engineering Data" module, this material will be translated to APDL commands along with other parts of the numerical analysis and saved in dat format. Then, This file will be sent to APDL solver to get analyzed and APDL results will be post processed again in Workbench. At the end of the day, this process shows that, even the material created in Workbench has to be translated in APDL commands and for that reason it is pointless to get access to Workbench "Engineering Data".