For starters, you could use classic divination methods. I tend to use different ones to find a common denominator in each of them. What comes through the strongest in different readings serves as my point of focus.
Edit: if you plan to consult a third party here, I would formulate the question as “What is currently going against my _ insert attacked aspects of your life _” instead of “Who is attacking me”. The reader is less biased that way and will be able to clarify the energetic nature of these attacks instead of pushing the description of a person into the reading for the sake of it.
If you are a bit firm with feeling energy signatures you could put that skill to use, as well 
If you’re into spirit workings I would suggest Andromalius. Ask him to expose the attacker, they usually tend to give themselves away.
If you simply wish to move on from this without focusing too much on “Who dunnit” I would suggest a Return to sender ritual. There are many approaches to this on this board, @crookedpathfinder shared a simple yet effective way here:
If you don’t have any clues and no tools at your disposal to securely identify the source of these attacks I would use the latter method first. Its easy to get caught up in wild guessing and attacking the wrong individuals; keeping a cool head is the dictate of the moment ESPECIALLY if you don’t have tangible proof about the attacker on your hands