A method and apparatus are disclosed from the perspective of a first device. In one embodiment, the method includes the first device performs sensing on a data resource pool, and the first device selects/derives at least a first data resource from the data resource pool based on the sensing result of the data resource pool. The method further includes the first device transmits a first control information on a first control resource, wherein the first control information allocates or indicates the first data resource. The method also includes the first device performs a first data transmission on the first data resource to at least one second device. Furthermore, the method includes the first device determines or derives a first set of feedback resource(s) based on the first control resource and/or the first data resource; and the first device receives a first set of feedback transmission(s) on the first set of feedback resource(s) from at least the one second device, wherein the first set of feedback transmissions are associated with the first data transmission.