"Kan jij" ofwel "kunt u".
Ja, kan ik.
Hij zei dat ik gelijk had. Ik zelf was ermee akkoord.
Ik was akkoord met zijn toestemming.
Ik was akkoord met/over het feit dat hij toestemde.
I would add, the rules for "er" in Dutch are difficult. It's not dissimilar in its mastery (not meaning) to "eben, halt, ja" in German. Even native speakers use it and cannot tell you WHY. The ONLY way to master it is as with so many things - stay attentive, listen, and learn to "feel" the language. Because rationalising it is not always the answer.
Last note: you can say "Dank U" to a relationship to whom you'd normally say "jij"; or you can say "dank je wel", but you must add the "wel". You cannot correctly use "Dank je wel" for an "u" relationship, but they'd unlikely be offended.
jij - dank je wel (or dankjewel) / dank u (or dank U)
u (or U) - Dank u/U or dank u/U zeer
The capitals for U and Uw/Uwe are becoming outmoded and a switch to lower case is normal.