Hello from JustAnswer.
There is no test that can readily detect the use of EpiPen days after the use. The epinephrine has a very short half-life, so blood tests to measure epinephrine would need to be done almost immediately after the injection to be able to detect the epinephrine. Metabolites of the epinephrine, called metanephrines, can be elevated for a longer period of time. These can be checked in blood tests or 24 hour collections of urine, but even these tests wold typically need to be done on the day that the drug was administered.
If it has been 6 days since the last adminstiration, there is no test that would be able to detect the drug.