This is not the only problem. After editing this line in Sconstruct I have my ReduceCpp compiled but after this when I try to use my ReduceCppTofCalib I get:

File "bin/my_test.py", line 39, in run
    MAUS.Go(my_input, my_map, MAUS.ReduceCppTofCalib(), MAUS.OutputPyJSON())
AttributeError: 'module' object has no attribute 'ReduceCppTofCalib'

also after typing in python:

import ReduceCppTofCalib

I get:

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/yordan/Workspace/maus/build/ReduceCppTofCalib.py", line 26, in <module>
_ReduceCppTofCalib = swig_import_helper()
File "/home/yordan/Workspace/maus/build/ReduceCppTofCalib.py", line 22, in swig_import_helper
_mod = imp.load_module('_ReduceCppTofCalib', fp, pathname, description)
ImportError: /home/yordan/Workspace/maus/build/_ReduceCppTofCalib.so: undefined symbol: _ZN11JsonWrapper12StringToJsonESs

My interpretation of this obscured error message is that I can't link with the things in src/common_cpp/Utils/

Karadzhov, Yordan wrote:

My interpretation of this obscured error message is that I can't link with the things in src/common_cpp/Utils/

That is correct...

How to fix this?

I'm investigating

Now is works for me too.
The thing that makes the difference was the line

require_g4 = True (False in my case)

in src/reduce/ReduceCppTofCalib/sconscript
Do I really need g4?

Probably this parameter should never have existed. Must be a lurking thing in SConstruct somewhere... are you ever going to try to compile MAUS without GEANT4? Just say "yes" I think...