Tellman Knudson told the world last September he would run barefoot the equivalent of a marathon a day from New York City to Los Angeles to raise $100 million for homeless teens. But after spending four months and $500,000 in road expenses to reach West Virginia, Knudson has returned to his Vermont home to “regroup.” He’s now facing questions about why his charity says it’s an officially registered nonprofit even though its name doesn’t appear on the Internal Revenue Service’s list of recognized organizations.