Once locked, you will see a green shield badge. Your existing friends will still see your content, but non-friends will see almost nothing.
The short, honest answer might frustrate you: The feature was designed specifically to prevent unauthorized viewing. how to see locked fb profile work
: This remains the only official way to gain full access to the user's timeline and "About" section. Once locked, you will see a green shield badge
If you need to see a locked profile, the only functional methods are grounded in social interaction rather than technical exploits: how to see locked fb profile work