In the s1e3 of Sherlock, the Great Game, Molly met James Moriarty at work. Jim from IT.
In s3e1 of Sherlock, the Empty Hearse, Molly emphasizes that she met Tom through friends, not through work. She sort of implies that meeting lovers through work isn’t trustworthy.
In the beginning of the same episode, as Sherlock deduces Mary Morstan, John’s (soon to be) fiancé. He deduces things such as liar, secret, disillusioned, and nurse.
A later scene shows Mary and John at work, together. Mary works as nurse where John works as a doctor. This somewhat, maybe, suggests that they met at work.