A person with knowledge of secret weapons puts themselves in a dangerous position.
Literal
Secret-weapons [possessive-の] knowledge [subject-が] exist person [topic-は], own body [object-を] dangerous position [in-に] is-placing.
秘密兵器の知識がある人 is a relative clause: 'a person who has knowledge of secret weapons.' 我が身 means 'one's own person/body.' ~を...に置いている describes the ongoing state of placing oneself in danger.