Sentence....question?

問題" Is there anything else I can help you with ( ? ) " 本身是正確的。

" can help " 無問題; 反而不可寫成 " can to help ".

can是 modal verb ( 即助動詞 ), can 後面可直接跟verb
例如 I can run, I can see, I can sing等等。

with 後面不用加東西, 因為 " help with " 是一組的。
help 當verb時的用法是 " to HELP somebody WITH something "
例如 Sam helps John ( somebody) with his work ( something ).
如果不指明幫人什麼時, with something 就可以省略,
例如 Sam helps John . <- 這也是一句正確完整句子。

將上面的問題轉成陳述句就會變成:
I can help you ( somebody) with anything else ( something ).
" is " 和 " there " 是因為要使陳述句變成句子才加上去的。