How to calculate the concentration of a K₂Cr₂O₇ solution?
First, you need a balanced equation for the oxidation.  The gives you the mole ratio of dichromate to substrate.  You know how many moles of substrate you have, you know how many moles of dichromate you need.  If you have 21.6 g of dichromate ions (as such)/liter, then you know how many moles/liter you have.  You know the number of moles you need, you know the number of moles/liter you have, you know the number of liters you need.

You will be doing your Jones oxidation in acid, of course.  Collins reagent is a sweeter deal for workup, since MEK is 27.5 g/100 ml water-soluble.