you looking to configured IP SLA in junper device, then you are in wrong forum.
if you looking to configure IP SLA on cisco device, Gatway is Juniper device. here is the guide how you can monitor :
(this is reference guide, you may have different product, but concept is same)
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipsla/configuration/15-mt/sla-15-mt-book/sla_icmp_echo.html