How can you reference taxonomy term by another field in Yaml file?
Here is a simple migration for looking up a taxonomy term by name based on the text in a CSV.

taxonomy_field_name:
  plugin: entity_lookup
  source: name_of_source_column
  value_key: name
  bundle_key: vid
  bundle: name_of_taxonomy
  entity_type: taxonomy_term


For example, if you have a taxonomy called fishes, and your CSV has a column called fish, and your node has a field called field_fish which is an entityreference to a taxonomy term of the fishes vocabulary, and there is a taxonomy term "Carp" with entity ID 14

field_fish:
  plugin: entity_lookup
  source: fish
  value_key: name
  bundle_key: vid
  bundle: fishes
  entity_type: taxonomy_term


Given a row in the CSV with "Carp" set as the fish, this will assign entity id 14 to that field.

Does that help?  I am not sure what you mean by "a given field can be referenced by any other field from my site".