The problem is the code and your sound, try:
Code:
#include < amxmodx >
public plugin_init()
{
register_plugin( "Plugin", "1.0", "Rejack" );
register_clcmd( "say /emit", "cmdEmit" );
register_clcmd( "say_team /emit", "cmdEmit" );
}
public plugin_precache()
{
precache_sound( "slash_hit_emit.wav" );
}
public cmdEmit( const client )
{
client_cmd( client, "spk sound/slash_hit_emit.wav" );
client_print( client, print_chat, "emitted sound." );
}