Where is ignorance, and why does it not end with death?
Ignorance is absence of right view. It's not tangible, as much as it is a lacking.
The buddhist notion of rebirth says that we're destined to samsara until sotapatti/"stream-entry" occurs to break the cycle.
Can we experience it?
The most tangible evidence of avijja/ignorance is dukkha/suffering.
Does it have to be actively conditioning formations for us to experience it, or can we know this nidana even when freed from it?
Regarding the first half of your question, ignorance is most likely conditioning formations in both a passive/and an active sense: Sometimes we end up in trouble without seeing it coming, and sometimes we end up in trouble because we deliberately ignore the consequences we have coming to us. These are two examples of how avijja may affect us.
Can't answer the last part of your question though. Sorry.