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

db.collection.aggregate([{"$unwind":{"path":"$rows","includeArrayIndex":"row_i"}},{"$unwind":{"path":"$rows.row","includeArrayIndex":"col_i"}},{"$match":{"rows.row":"345"}},{"$project":{"_id":0,"value":"$rows.row","row_i":"$row_i","col_i":"$col_i"}}])