Include the tags field migration.

web/modules/custom/agaric_migration/migrations/agaric_blog.yml

@@ -2,7 +2,7 @@ id: agaric_blog
 migration_group: agaric
 label: Agaric Blog
 source:
-  plugin: d7_node
+  plugin: agaric_node
   node_type: blog
 destination:
   plugin: entity:node
@@ -61,6 +61,18 @@ process:
     plugin: migration_lookup
     source: node_uid
     migration: agaric_people
+  field_tags:
+    plugin: sub_process
+    source: field_tags_names
+    process:
+      target_id:
+      - plugin: entity_generate
+        source: name
+        value_key: name
+        bundle_key: vid
+        bundle: tags
+        entity_type: taxonomy_term
+        ignore_case: true
 migration_dependencies:
   required:
     - agaric_people

web/modules/custom/agaric_migration/src/Plugin/migrate/source/AgaricNode.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace Drupal\agaric_migration\Plugin\migrate\source;
+
+use Drupal\migrate\Row;
+use Drupal\node\Plugin\migrate\source\d7\Node;
+
+
+/**
+ * Add the Taxonomy term name in the query.
+ *
+ * This adds the sourceProperty field_tags_names which are the name of the terms
+ *
+ * @MigrateSource(
+ *   id = "agaric_node",
+ *   source_module = "node"
+ * )
+ */
+class AgaricNode extends Node {
+
+  public function prepareRow(Row $row) {
+    $nid = $row->getSourceProperty('nid');
+    // Get the taxonomy tags names.
+    $tags = $this->getFieldValues('node', 'field_tags', $nid);
+    $names = [];
+    foreach ($tags as $tag) {
+      $tid = $tag['tid'];
+
+      $query = $this->select('taxonomy_term_data', 't');
+      $query->condition('tid', $tid);
+      $query->addField('t', 'name');
+      $result = $query->execute()->fetchAssoc();
+      $names[] = ['name' => $result['name']];
+    }
+    $row->setSourceProperty('field_tags_names', $names);
+
+    return parent::prepareRow($row);
+  }
+
+}