[LearninG]

#include <amxmodx>

public plugin_init()
{
    register_plugin("query client cvar example" , "1.0" , "LearninG")
    register_clcmd("say /test" , "test")
}

public test(id)
{
    query_client_cvar(id , "cl_righthand" , "Handler")
}

public Handler(id , const szCvar[] , const szValue[])
{
    new value = str_to_num(szValue)
    client_print(id , print_chat , "[AMXX] cl_righthand is %d" , value)
}

if you want to check the value :

if(value == 1)
{
    //do your code
}
else
{
    //do your code
}