Edelgard would be interested to see some of his memories of Garlemald. The ceruleum stuff might be interesting, as it would give her insight into what Garlemald was like before it transitioned into the Empire, but the stuff regarding his son (especially his death) would be a point of commonality for them (both having lost family and it having a drastic effect on their characters).

Or if you have an Emperor HC that might be of interest to Edelgard, that would also be good!