In this page of dotPeek options, you can define settings of the dotPeek symbol server.
Generate symbol files (.pdb) for:
Using the radio buttons, choose assemblies for which symbol files should be generated. The meanings of the first four options are obvious. The last one allows for the most flexibility — after selecting this option, you can select only those assemblies which you need for debugging, and open them in the Assembly Explorer.
dotPeek symbol server port. You may need to change the default port number if it is occupied by other application.