CREATE TABLE table_26919 ("Round" FLOAT, "Circuit" TEXT, "Date" TEXT, "Pole Position" TEXT, "Fastest Lap" TEXT, "Winning Rider" TEXT, "Winning Team" TEXT)

How many dates was knockhill?
SELECT COUNT("Date") FROM table_26919 WHERE "Circuit" = 'Knockhill'
SELECT COUNT("Date") FROM "table_26919" WHERE "Circuit" = 'Knockhill'