" Nor Indeed what to say " 省略倒装句．　完整的句子应该为：　Nor had I indeed the slightest doubt as to what I was to say .

特别是：　as to what I was to say 不知如何理解？　　　I was to say 　也不符合语法．

as to表示：关于, 至于，相当于about
Nor had I indeed the slightest doubt as to what I was to say.
相当于I didn't have the slightest doubt about what I was to say.

整句话表示：我对我接下来所要说的话一点也不怀疑。


Nor提前，所以用部分倒装。整句话语法上没有错。因为前面谓语动词就是have的过去时had，所以I was to say是我对过去发生的下一刻所要说的。