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If you are in taxonomy page.
That’s how you get all details about the taxonomy.
get_term_by( 'slug', get_query_var( 'term' ), get_query_var( 'taxonomy' ) );
This is how you get the taxonomy id
$termId = get_term_by( 'slug', get_query_var( 'term' ), get_query_var( 'taxonomy' ) )->term_id;
But if you are in post page (taxomony -> child)
$terms = wp_get_object_terms( get_queried_object_id(), 'taxonomy-name');
$term_id = $terms[0]->term_id;
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