Storj Labs cannot make specific recommendations of which exchange you should use, but you can find the exchanges that trade the STORJ token listed here.
In most countries except maybe Korea, you would have to first convert STORJ to either Bitcoin or Ether and then trade those for your local currency at a cryptocurrency exchange that operates in your country. Be aware that centralized exchanges will most likely require you to first pass KYC requirements before you can start trading. You can at least make the first step a bit less painful if you use a swapping service like https://changenow.io https://coinswitch.co/ and /https://changelly.com/ and more which let you just specify your sending STORJ address and receiving BTC or ETH address and make the swap almost instantly. This is more convenient than using an exchange, but it may involve a slightly higher fee (the price of the convenience).
You can try first with a small amount of STORJ if you are not sure how it works at first. In any case, please do not leave your tokens, BTC or ETH for extended periods of time on a centralized exchange that does not let you hold your private keys yourself. All exchanges can be targets of hacking attacks at any time, so best to just complete your trade quickly and withdraw your funds to your own wallet or bank account. Also, before you use a centralized exchange that works for your country, be sure to find out if they have any restrictions on how much or how fast you can withdraw your funds, if this requires KYC and what fees they will charge, otherwise you may have some unpleasant surprises later. Please use the exchange services' support forums for further help, we cannot give you support here for all the existing exchanges in the world, that is outside the scope of this project.