I am running test cases using robot --include smoke /
I need smoke tag which was passed in command line argument in test case.
The current tags are available in the Test level through the built-in variable ${TEST TAGS}
; you can iterate over its members to see what the case has:
FOR ${tag} IN @{TEST TAGS}
Log tag: ${tag}
END
Yet that will give you all tags a case has assigned; so in your case it will return "smoke", but will also return "sanity", "feature" and all others it might have.
There's no exposed user-level variable/keyword to get what exactly were the tags set for the current execution; using the RF API you may be able to get a reference to the current execution context and access such property (if it's present).