There is no easy way here, but if you have the enabled the SQL server you use to log every single sql statement, here is what I would do.
Normally, when I SQL inject somewhere, i use one of these as my always true statement for passing throgh the Where clause, after ending the former string.
1=1
0=0
both being used as :
blahblahblah or 1=1 --
You would not use this clauses in everyday code. So if you spot one of these in your history, well, it is a high candidate. Test the sql history to find :
(space)(number)(optional spaces)(equal)(optional spaces)(same number)(space)
Keep in mind that is heuristical, and will not always work, but could be the only way to give a hint after it had happened . Also, if you are in doubt about SQL injection, you should check the code for string concatenation and use of parameters.