I hope there is some better way of doing it, or better tooling, because I also struggle with this and it makes the development tedious. For now what I am doing is:

Note: You need the complete sources including the addons. Also I am doing this for LTS2019 but the process should be the same.

1. Find the corresponding java file in the sources i.e. ./nuxeo-features/nuxeo-platform-task/nuxeo-platform-task-api/src/main/java/org/nuxeo/ecm/platform/task/TaskService.java
2. open the the associated pom.xml i.e. ./nuxeo-features/nuxeo-platform-task/nuxeo-platform-task-api/pom.xml
3. note the parent group id org.nuxeo.ecm.platform and the artificatId (not the parent one) nuxeo-platform-task-api
4. Add these as a dependency in your pom.xml

   <dependency>
     <groupId>org.nuxeo.ecm.platform</groupId>
     <artifactId>nuxeo-platform-task-api</artifactId>
   </dependency>
   

   If you specifiy nuxeo (e.g. nuxeo-addons-parent) as your parent you should not need a version tag (e.g. <version>10.10</version>).

But: More often this is not enough and you keep doing these steps again and again for different missing dependencies. Sometimes there is a parent artificat that is more appropirate to use instead of listing all the single dependencies.