Staking rewards are allocated each era, but there is a manually step that needs to occur in order to receive the rewards, the reward payouts need to be initiated for each validator in each era. As soon as a validator or staker requests a payout for an era, all the stakers for that validator will receive the rewards into their accounts. Each user does not need to claim individually and it is recommended that validators claim rewards on behalf of their stakers as soon as an era ends. Reward payouts for can be initiated by any account.
Dock stores up to 84 eras of reward information so rewards will not be claimable more than 84 eras after they are earned. This means that all rewards must be claimed within 84 eras. You can check an explorer to see any historic payouts made to your accounts.
To claim rewards on the DockJS UI, you will need to navigate to the Payouts tab underneath Staking, which will list all the pending payouts for your stashes. To then claim your reward, select the Payout all button. This will prompt you to select your stash accounts for payout.
Once you have selected the stash account, another screen will appear asking for you to sign and submit the transaction.