As a player how do I determine the level of NPC‘s?

[blackjack50]

This is something I am still struggling with. In my last campaign there were a few NPCs who definitely deserves to be hit but I hesitated because of their level. Hey seemed extremely high level but just as easily could have been at my mercy. Any good methods for this?

[Aett_Thorn]

Away from book right now, but I think that both Battlemasters and Mastermind Rogues get abilities that allow you to determine relative hit die of creatures.

Otherwise, not sure how to tell exactly other than DMs telling you.

[Guy Lombard-O]

Battlemaster 7th level feature

Detect Thoughts or divination spells to get general idea of their combat experience of overall dangerousness.

Keep in mind that they may not even have levels, but have stat blocks like monsters do.

Overall, you're taking a risk by attacking NPCs. You'll just have to gauge whether it's a good idea (for legality, individual or situational dangerousness, etc.) based upon how the campaign unfolds. So, don't be a murder hobo without a care for the consequences.

[Ventruenox]

Well, there is the Mystic (https://media.wizards.com/2017/dnd/downloads/UAMystic3.pdf) who has the Assess Foe ability.
(2 psi). As a bonus action, you
analyze the aura of one creature you see. You
learn its current hit point total and all its
immunities, resistances, and vulnerabilities.

Or just play how your character would react and see what happens.

[Addaran]

Others have mentionned the mechanical ways.

If they are a caster, knowing the highest lvl spell you've seen them do can help.

Asking In-Character about the person might also help. If they are known to be a powerful warrior, a good duelist or there's a story how they fought of a pack of orcs ( or a dragon). Or you could learn he's a coward always running away,

[Dakael27]

If he deserves to be hit just hit em!

If I worried about picking fights with people stronger than me in real life I'd have less scars sure, but the story would've been a hell of a lot less interesting!

[Yakk]

Is your character an idiot who gets killed by hitting everyone who deserves it? Then roleplay it, and die.

First make sure your table is ok with that.

Otherwise, you hit someone when you think the risk of death is worth the job.

[MaxWilson]

This is something I am still struggling with. In my last campaign there were a few NPCs who definitely deserves to be hit but I hesitated because of their level. Hey seemed extremely high level but just as easily could have been at my mercy. Any good methods for this?

Try asking around, trying to suss out his reputation and/or any impressive deeds he's known for. Does he go on dinosaur hunting trips and come back with T-Rex skulls? Then he's not a 3rd level chump. If you DM allows you to pay NPC sages for answers, you can also try asking them.

Alternately, you can try consulting an Augury or Divination spell: "Will it be good or bad for me if I start a fight with this guy?" Weal = he's probably weaker than you, woe = he's either stronger or there would be other negative consequences if you beat him up (angry friends, etc.).

Finally, you could find ways to test it out directly: challenge him to a "friendly" duel, 50 gp to whoever draws first blood, for example. Remember, he doesn't know your capabilities any better than you know his.

[blackjack50]

Battlemaster 7th level feature

Detect Thoughts or divination spells to get general idea of their combat experience of overall dangerousness.

Keep in mind that they may not even have levels, but have stat blocks like monsters do.

Overall, you're taking a risk by attacking NPCs. You'll just have to gauge whether it's a good idea (for legality, individual or situational dangerousness, etc.) based upon how the campaign unfolds. So, don't be a murder hobo without a care for the consequences.

No murder hobo stuff. When someone is going to be facing violence from the group...it is best to hit first, fast, and from where it isn’t expected. Violence of action is a good policy if you are dealing with pirate scum or whatever other kind of evil they might be.

[KorvinStarmast]

Is your character an idiot who gets killed by hitting everyone who deserves it? Then roleplay it, and die.

First make sure your table is ok with that.

Otherwise, you hit someone when you think the risk of death is worth the job. Heh, this answer made me chuckle.

Waterdeep Dragon Heist has a number of NPCs who are way out of the league of a group of 1-4 level players.