The standard cup of coffee sold in coffee shops have a serving size of 6 ounces. Since there are 28.3495 g in 1 oz, that is equivalent to 170.097 grams. Since you drink two servings, the total mass is 170.097×2 = 340.194 g. Using the molar mass (194.19 g/mol) and the Avogadro's number (6.022×10²³ molecules/mol):
340.194 g caffeine(1 mol/194.19 g)(6.022×10²³ molecules/mol) = 1.055×10²⁴ molecules
