Answer
False
Work Step by Step
We have $T_2$ is onto.
Suppose $T_2(x,y)=(x,y)$
Define: $T_1(x,y)=(0,0)$
We know $ T_1 : V_1 → V_2$ and $T_2 : V_2 → V_3$ are linear transformations
obtain $(T_2T_1))(x,y)=T_2(T_1(x,y))=T_2(0,0)=(0,0)\\
\rightarrow Rng(T)=(0,0) \ne R^2$
Hence, $T_2T_1$ is not onto.