I need REST api for list datagroup and check the irule is applied to which vs

An alternative would be to use plain tmsh. The example below (one-liner again) does a recursive search to cover all admin partions and folders:

$ tmsh -q -c "cd /; list ltm virtual recursive" | tr -d '\n' | sed -r 's/([^[:space:]])}/\1}\n/g' | \
tr -s '[:space:]' | sed -r 's/([^[:space:]])\}/\1 }/' | \
grep -Eow '(virtual [^ ]+|rules (none|\{[^\}]+\}))' | tr '\n' ';' | \
sed -r 's/;$/\n/; s/;(virtual )/\n\1/g'
virtual Common/vs_51;rules { Common/rule_remove_xff Common/rule_plaintext }
virtual Common/vs_52;rules { Common/rule_remove_xff }
virtual Common/vs_53
virtual Common/vs_54;rules { Common/rule_plaintext }
virtual Common/vs_55
virtual myadminpartition/myiapp.app/myiapp_redir_vs;rules { myadminpartition/myownfolder/rule_myredirect }
virtual myadminpartition/myiapp.app/myiapp_vs

The output above lists as well the strange case of using folders (by iApp and own) in an administrative partition.