Scusate la lunga assenza prima della risposta. Il mio problema l'ho risolto, esattamente in questo modo:

codice:
$.each( data, function(id,file) {		
			 $("#maincontent").html("");
			var fileDetails = $("<p>").html("<b>Nome file:</b> " + "<a href='#commentTextID'>" + file.original_name + "</a><b> Consegnato il: </b>" + file.uploaded_at +
			"<b> Commento: </b>" + file.comment).attr("data-id",  id).attr("data-hash", file["hash"]); 		     
			 fileDetails.click(function(){
				 $("#fileNameComment").html("");
				 var details = $(this);
				 idFileToComment = details.attr("data-id");
				 hashFileToComment = details.attr("data-hash");				 
				 $("#fileNameComment").append("Add comment for " + file.original_name);				 
				 console.log(details.attr("data-hash"));
				 });			
			$("#filesField").append(fileDetails);					
			});	
	 }else{		 
		 alert("Nothing uploaded for this assignment.");		
	 }