Feedback in workplaces is usually sugar-coated. Managers, peers, and mentors hedge with positives to soften criticism. Asking explicitly for 'your honest assessment of where I'm at' often unlocks genuinely useful information that wouldn't otherwise be shared.
How to ask
Specific question, not vague. 'What's your honest assessment of where I'm at against promotion criteria?' or 'What's the single biggest thing holding me back?' Specific framing produces specific answers.
Who to ask
Manager (most useful for current role). Senior peer who's seen your work. Former manager who knows you well. Mentor with broader perspective.
Resilience required for the answers — you'll hear things you didn't want to. Most ambitious professionals find the answers worth the discomfort.