Will a 3.5mm headset splitter work with my office headset?

Only if your office headset uses a 3.5mm jack (similar to a headphone jack on a phone). Most professional office headsets use QD (Quick Disconnect) or USB connectors. However, if you have a headset with a 3.5mm plug, a 3.5 mm headset splitter is exactly what you need to connect two of them to a single device.