How I can view facet view key?
It's delta of block.
You can receive it via this code:

$delta = facetapi_hash_delta(facetapi_build_delta('SEARCHER@MACHINE_NAME_OF_SEARCH_INDEX', 'block', 'MACHINE_NAME_OF_FACET'));


Example:

$delta = facetapi_hash_delta(facetapi_build_delta('search_api@fr_node_index', 'block', 'field_price'));