You can earn interest on BTC by investing it (Which is not necessarily accomplished by just investing it, the asset also has to perform) on any reputable platform you can find, or through holding it somewhere that offers interest like poloniex or other services.

Alternatively, if you feel like loaning it is a better way to do it, sites like BTCJam seem reputable right now, so you can look at those and aim to loan our some of your Bitcoin.

Make sure to do your own research, though. I am not telling you what to do, just giving you ideas.