Measuring temperature with a thermocouple works by measuring the voltage between the two signal wires, made from two different metals, let’s call them A and B.
To calculate the temperature at the "hot junction" from this voltage, you have to measure and compensate for the temperature at the "cold junction" i.e., where the wires made from materials A and B are connected to the copper wiring in the DAQ card. Usually there is a temperature sensor inside the DAQ card for this purpose.
If you want to use the WF3132 to multiplex the signal, this means that the cold junction will move to the input connector of the WF 3132. If the temperature of the WF3132 is similar to inside the DAQ card, the measurement errors introduced should be small.
There are also other junctions within the WF3132 that could have an impact on the measured voltage, but if you wire both signal leads through the WF3132, they will cancel each other out.
Following is an example showing how you could wire 16 thermocouples (TC0 - TC15) to one analog input on a DAQ card (AI0+, AI0-) using one WF3132:
