TLDR: Yes, you can always pinpoint someone's location as long as they're not actively hiding

This is an amalgamation of a few rules that, when taken together, end up with the conclusion that everyone in combat knows exactly where everyone else is.

First, this is what happens when you try to attack a creature that you can't see (SRD p. 94, "Unseen Attackers and Targets"):

When you attack a target that you can’t see, you have disadvantage on the attack roll. This is true whether you’re guessing the target’s location or you’re targeting a creature you can hear but not see.

Backtracking a bit, think about how ranged attacks in 5e work. Archers simply need to see their target and they can attack normally. If an archer is deafened, they can still target a baddie 50 yards away without penalty. The only thing the 'deafened' condition applies is (SRD p. 192, "Deafened"):

A deafened creature can’t hear and automatically fails any ability check that requires hearing.

So the only thing necessary for an archer to attack an enemy is that they can see the enemy. Seeing them allows them to know where the creature is to the square, allowing them to make their attack without disadvantage. Archers also don't have to worry about sporadically missing their shots because they picked the wrong square to attack, so we know that seeing an enemy is all that is required to know their square.

Now let's apply that to the SRD passage. If the creature you're attacking doesn't know where you are, you automatically get advantage against them. However, getting advantage (without hiding) by not having a creature know where you are is relatively rare in combat. Thus, if most creatures in combat did not know where the other ones are by default, then most attacks would be made with advantage, which clearly doesn't happen. The only way to have combat proceed normally (where most attacks don't get advantage due to being unseen) would be that every creature has a good visual awareness of the other creatures without having to do anything special to achieve it. Couple this with our above archer example where we were able to infer that visual awareness is sufficient to know the location of a creature, and you get the first part of the argument which is 'creatures in combat see all other non-hiding creatures in combat'.

So we now know that in combat, the rules expect that everyone sees everyone else. What about positioning and direction? This is covered also in the SRD pages 80-81 ("Hiding" sidebar):

In combat, most creatures stay alert for signs of danger all around, so if you come out of hiding and approach a creature, it usually sees you.

Again, we see that most creatures are aware of their 360* surroundings in combat, and even approaching from behind or the sides is not enough to evade their detection. The only way for this to be possible would be for the creature to know where you are, because as we saw earlier, not knowing where a creature is means that the creature automatically has advantage on you, which does not happen in this case.

Finally, what if the target is behind a wall and completely unable to be seen, but is not hiding? The rules have a section for that as well under 'total cover' (Basic Rules p. 74, "Total Cover"):

A target with total cover can’t be targeted directly by an attack or a spell, although some spells can reach such a target by including it in an area of effect. A target has total cover if it is completely concealed by an obstacle.

So in this case, since the target is not hiding, we cannot see them but we can hear them. This goes back to the Unseen Attackers rule (SRD p. 94, "Unseen Attackers and Targets"):

When you attack a target that you can’t see, you have disadvantage on the attack roll. This is true whether you’re guessing the target’s location or you’re targeting a creature you can hear but not see

So if we cannot see a creature but we can hear them, we can attack them with disadvantage. Since attacks where we cannot pinpoint the location of the creature automatically fail, we know that hearing the creature is enough to pinpoint their exact location.

So putting all this together, we see that a creature in combat can see every other creature in combat as long as they're not hiding (otherwise pretty much everyone would attack with advantage every turn), seeing someone is all that's necessary to attack them normally (otherwise ranged attacks would be impossible or always made at disadvantage, and being deafened would affect ranged effectiveness), hearing but not seeing someone still allows you to pinpoint their location (otherwise total concealment would make it impossible to attack someone and not just impose disadvantage), and attacking a creature without disadvantage or potentially automatically missing means you must know their exact location (otherwise you would trigger the 'Attacking unseen targets' rule and miss by default). So because the situations in parentheses above don't actually happen, we know that all creatures know the exact location of all other creatures unless one of them is hiding.