Citing data can be challenging, as citation style guidelines are not always well-suited to data formats. For data you find online, a good rule of thumb is that your citation should allow someone to find the data you're citing, even if the URL you provide in your citation stops working.
In general, all data citations should include the following elements:
Author or creator
Year of publication and/or last update
Title or description
Publisher or distributor (database, repository, etc.)
Unique identifier (URL or DOI)
Any other elements the creator or publisher asks you to include
Consult the guidelines for your citation style to determine how to format these elements.