1)You need add an analyst scout them before each match:
Scouting -> Scouting coverage drop down menu -> Match & Team Analysis
2) Search the team you are facing . When you get in their profile go to team reports > senior squad analyst report
You will get there Formations Used & Faced. The formation created the most clearcut chances against them is the one you are looking for.
Also you can ask a report for the team you want and on "red" side of the team report the scout will say their weakest spot & the formation they conceded the most against.