「もう一歩（だ）」 literally means "(You need to go) one more step (to reach the desired level)". It's like "(You're almost there but) just one step away from the desired level". It can be rephrased as 「もう少し」, 「あと一歩」, etc.
The ところ is used for 抽象的な場所 (abstract place) and can mean "stage", "level" or "condition". ～といったところです literally means "in the stage/level that you'd call..." i.e. "you're around the level/stage that is..." (といった sounds a bit more reserved/indirect and less assertive than という.) ～といったところ can practically mean "around~~" "approximately~~" "something like~~" "I'd say~~", e.g.
So 「漢字はもう一歩といったところです」 literally means "As for your kanji, you're in the stage where you'd need to go just one more step (to reach the desired level)", or "As for your kanji level, (you're almost there but) it's just a step (behind the desired level)".
Additional Info: For reference, A Dictionary of Advanced Japanese Grammar explains this phrase as: "A phrase the speaker/writer uses to explain something in a brief/rough manner. I would say ~; ~ is how I’d put it" (page 633).