Tenses can sometimes get very tricky. This appears to be one such case. Attempting to bail you out of this 'tense morass'.
I knew I asked the right person.
Your knowing and asking are simultaneous actions.
I knew I had asked the right person.
This is what they call pluperfect in the English language.
Here two past events are involved: your knowing and your asking the right person.
In cases where two past actions are involved, one must precede the other (for otherwise we would need a different tense to describe the situation). Here your asking the right person precedes your knowing about it (maybe as an afterthought when everything went well).