。
Can I see the lawyer on Friday?
Literal
Lawyer-honored [with-に] Friday [on-に] can-meet (polite)?
弁護士さん adds さん to a professional title — a respectful but familiar way to refer to someone by their role. Common with 'お医者さん,' '八百屋さん,' '郵便屋さん.' 会える is the potential of 会う ('can meet'); 会う takes に for the person met.