Which among the following chemical equations represents a non-metal...

In a non-metal displacement reaction, a non-metal displaces another non-metal from its compound.

In the reaction $Cl_2 + 2KBr \rightarrow 2KCl + Br_2$, chlorine ($Cl_2$), which is a non-metal, displaces bromine ($Br_2$), another non-metal, from potassium bromide ($KBr$). Therefore, this is a non-metal displacement reaction.

For the other options:
$TiCl_4 + 2Mg \xrightarrow{\Delta} Ti + 2MgCl_2$ is a metal displacement reaction since magnesium displaces titanium.
$2NaH \xrightarrow{\Delta} 2Na + H_2$ is a decomposition reaction.
$4H_3PO_3 \xrightarrow{\Delta} 3H_3PO_4 + PH_3$ is a disproportionation reaction.

Answer: $Cl_2 + 2KBr \rightarrow 2KCl + Br_2$