There are $4$ possible cases :-
Case $1)$ Both $A$ & $B$ are knights
Now, both statements from $A$ and $B$ will be true which will not be contradicting our assumption. So, Both $A$ & $B$ are knights is a possibility.
Case $2)$ $A$ is knight & $B$ is knave
Now, $A$'s statement "I am a knight" is true which means $A$ is knight and $B$'s statement "I am a knight" is false which means $B$ is knave. Both are not contradicting our assumption. So, It is also a possible case.
Case $3)$ $A$ is knave & $B$ is knight
Now, $A$'s statement "I am a knight" is false which means $A$ is knave and $B$'s statement "I am a knight" is true which means $B$ is knight. Both are not contradicting our assumption. So, It is also a possible case.
Case $3)$ $A$ is knave & $B$ is knave
Now, $A$'s statement "I am a knight" is false which means $A$ is knave and $B$'s statement "I am a knight" is false which means $B$ is knave. Both are not contradicting our assumption. So, It is also a possible case.
So, Answer is :- We can't determine what $A$ and $B$ are which means $A$ can either be knight or knave and $B$ can either be knight or knave.