Which teams could Liverpool face in the Round of 16 (knockout stages) of the 2020/21 Champions League?

LFC could face any of these seven opponents- Borussia Monchengladbach, Barcelona, Atletico Madrid, Sevilla, FC Porto, RB Leipzig, Lazio

These seven finished as runners up of their group. All English teams won their group and Liverpool cannot face the runner-up of their own group (Atalanta), so their Round of 16 opponents will be from one of the seven above.

Can Liverpool face Man City or Chelsea in the UCL Round of 16?

No, teams from the same association cannot face each other in the Round of 16. Also Chelsea and City both won their groups, so they are seeded (as are LFC), and a group leader can only play a group runner-up (unseeded)