If you have locked DOT in your account (because you e.g. bonded them for voting, or you bought locked DOT during a token sale) then you can check on polkadot.js when they will become available. 

Simple open your account page and look up your balances:

Then hover your mouse over the (i) next to vested. You will be shown at which time and which block your DOT will become available:

Tokens from the sale in July 2020 will be vested at block number 3,281,096 mid January 2021 (5 months after the transferability date, which was August 18, 2020) as per the sales agreement. 

Once the vesting period is over, click on the three dots next to your account and select "Unlock vested amount" in order to unlock them and be able to transfer them.