Direct and indirect Links
There are two types of links: direct links and indirect links. Only test cases can be indirectly linked to requirements.
Direct links and indirect links are summarized in the #TCs column of the Requirements view. A small green triangle at the right upper-corner of the #TC field signals that there is at least one test case with a link inherited from a variant. Hover with the mouse over the field to see how many test cases are directly and indirectly linked to a requirement.
One directly linked and two indirectly linked test cases
Direct link
When you select a test case, variant, or assesslet and link it to a requirement, this is regarded as direct linking. Directly linked items are listed in the Linked objects section of the Requirements view.
Test case directly linked to two requirements
Test cases, variants, or assesslets that are directly linked to a requirement change their icon appearance in the Project view and respectively in the Assesslets view in that it displays a little arrow and a small number. The number tells you to how many requirements the item is linked to. For example, an unlinked test case 
would change to 
if it would be directly linked to two requirements.
Direct links are mentioned in the Report Linked Requirements section in the test case specific part of the test report in the column Linked.
Test case directly linked to a requirement shown in the test report
Direct links are also listed in the Usage view, see Views - Usage.
Indirect links
When you link a variant to a requirement, the test case that uses this variant inherits the link to the requirement.
Indirect links are mentioned in the Report Linked Requirements section in the test case specific part of the test report in the column Linked as "indirectly via <path to the variant>".
Test case indirectly linked to a requirement shown in the report
A test case that inherits the requirement link from a variant does not show a small number at its icon; only the number of direct links are displayed as an overlay. It is also not listed in the Linked objects section of the Requirements view.
A green triangle in the row of the #TCs column means that some test cases are indirectly linked to the requirement
So, to find out which test cases have inherited links from a directly linked variant, go to the Linked objects section of the Requirements view and double-click on the variant listed there. This will select the variant in the Project view. Next, right-click on the variant, then go to Used by|Test Cases.
Indirect links are also listed in the Usage view, see Views - Usage.