depending on which flight you could be at either the C or D gates. unfortunately they are quite far from each other (~15 minute walk maybe?) but the BA / QF lounges are at the C gates while Dnata is at the D gates.

if you get a chance though, definitely try out the BA lounge. Food is meh but it has an amazing bar and really nice ambience. Dnata lounge as mediocre bar and mediocre food so it's not my favourite place all around -- if that's the only lounge you can visit you are probably better off spending an extra half hour in Singapore city itself (the trip to the airport isn't long, immigration queues tend to be short, and security is at the gate vs. before immigration)