Deadlock Detection | Should the node T4 point to T1 and T2?
T4 is only requesting B, which is held by T2. The line represents the dependency on the resource from a requestor to a holder; the graph does not model a &quot;queue&quot; of waiters, that's a different problem.
To help understand the graph draw the 4 processes T1-T4. Each time a resource is granted to a process, put the letter next to it. When you realize a process needs a resource held by another process draw a line from the waiter to the holder.
So in order:

T1 is granted A
T2 is granted B exclusively, T1 requests B. Draw a line from T1 to T2.
T3 is granted C
T2 requests an exclusive lock on C which is incompatible with the shared lock held by T3. Draw a line from T2 to T3.
T4 requests requests an exclusive lock on B which is held by T2. Draw a line from T4 to T2.

This is not a deadlock, btw.
If this helped you, please don't forget to mark this as solved; thank you.