[{"rows":[["123","234","345","345"],["345","456","567"]]},{"rows":[["111","222","333"],["444","555","345"]]}]

db.collection.aggregate([{"$unwind":{path:"$rows",includeArrayIndex:"row_i"}},{"$unwind":{path:"$rows",includeArrayIndex:"col_i"}},{$match:{"rows":"345"}},{"$project":{"value":"$rows","row_i":1,"col_i":1}}])