Off the top of my head, that is a notice, that is sent by the sender of the file just prior to them sending the file.
So you likely have turned off showing notices in active channel alt-o/irc/show in active:[notices]
you can also however actually tap the DCC send message itself for the IP (which might be different from the notice (can happen but not often))
alt-r/file/new/enter following line
CTCP *:DCC SEND*:?:{ echo -at ATTENTION: $nick is sending you a file called $nopath($filename) from $longip($getok($1-,-3,32)) ip. }
