Is the dry, dull, slightly raised part of the toe, which is fully connected to the skin, dead scurf or what?

"Qashaf" is dryness of the skin. If part of a finger is dry and hard, and its removal does not cause you hardship, then it is considered as if it were separate. Wudu (ablution) is not valid with its presence if it prevents water from reaching the skin. However, if its removal causes pain, then wudu is valid with its presence, and its removal is not necessary.