usually someone in the group will ask him what the preference of expressing condolence is... For coworkers, you are not expected to be at the wake unless you are very very close personally. Based on what they tell you, you can send flowers to the funeral home, to their family (assume the address is shared with you) or send money to certain charity (a lot of people do that), or go with the big group signing a card. If sending flowers, just pick one recommended for funeral.