JPMS supports multiple layers. For example boot layer and its two child layers.
And I need to show these layers on UML diagram. For this I selected component diagram where every layer is a component. And my question is what arrows I should use to show relations. I think about dependency arrows:
but I am not sure. Could anyone say what arrows should be used in this case?
Your assumption is correct: dependency arrows should be used. The direction of a dependency arrow is from the dependent component to the component on which it depends. In this case, Child 1 and Child 2 require Boot layer to be present.
To clarify the relationship even more, you could attach stereotype «use» to both arrows. The UML 2.5.1 specification, section 7.4.4 says: "A Usage is shown as a Dependency with a «use» keyword attached to it."