Where is profit made from the purchase and subsequent redemption of a property tax lien reported?

[MaryK4]

You would report the sale of the property as "Sale of an Asset".  You can add the property tax lien and any other expenses as the basis, which will be subtracted from selling proceeds you receive.  See How do I enter the sale of land?

[Critter-3]

If you get back what you paid  for the lien  + interest then you only have to report the interest on the Sch B ... it doesn't go on the Sch D.