Sc border around waffle stitch

[Nicolapen]

I have done a sqaure of waffle stitch. For the border you start by working 2 SC in the corner then SC in each stitch across

Where should i put my hook to do 2sc in corner?

My last stitch i did DC in top of turning chain

[Granny Square]

Sometimes you just have to improvise.  You are right, there is no perfect spot in the corners (which would be at a 45° angle) for a pattern worked in rows.  I usually choose to put the corner in the first and last stitch of the last row, and the first and last stitch of the underside of the first row.  That doesn't make my choice right (but it's a consistent choice, if that makes sense).  

Comment - most references I've seen say to put 3 SC in the corner (or 5 DC, if that's the border stitch you are using).  For either of those, I use a chain for the middle stitch, the chain makes the corner turn cleaner, with less bulk.  The 3 stitches that compress a little might make up for that 45° angle thing too.