Trespass laws vary dramatically between jurisdictions. As a process server, you are responsible for knowing exactly what you are and are not permitted to do.
Normally, approaching someone's front door in order to knock is not considered trespassing. However, if the property is fenced and gated, then climbing the fence or jumping the gate would be considered trespassing and if the person lives in an apartment complex or gated community, technically, the entire building or complex can be considered private property and you'd need to wait for the gate to open before going through.
If you can't serve the guy without hopping a gate, then don't do it and tell your boss to either pay you to sit and wait for the gate to open, or file for alternative service or service by publication, like everyone else.
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