Right now, I already got the value "field_application_type." How can I get the lable "application type"(in the red circle) for this machine name(in the blue circle)?
The correct way to obtain a Label of a taxonomy vocabulary would be something like this:
$vocabulary = taxonomy_vocabulary_machine_name_load('machine_name'); echo check_plain($vocabulary->name);
However, looking at your screenshot, I guess you actually want to have the field Label of the taxonomy reference field.
In that case your question is a duplicate of How do I get a field label by the field name?