Hi @ChereeKr!
First, I’d like to tip my imaginary hat to you, because understanding why and how we apply the different pronouns is more than half of the Pronomen-Marathon! 
But I feel you - I’m sure that everybody who’s learning a new language went through a similar rough patch at one point or another… 
You are not alone in this!
To internalize those rules and get as comfortable as possible with them is like running the last miles of this marathon. So don’t give up! 
Every lesson, every try (and yes, every failure, too!) is one (baby-)step in this marathon! And behind the next corner (a.k.a. LL), there might be a runners high waiting for you! 
Enough with the bad metaphors! 🤦🏻😅
If students know how to differentiate the cases and their objects, they usually get way better at using the correct pronouns.
Unfortunately, there are a lot of different types of pronouns in the German language (7 different subsets), but let’s stick to the personal pronouns for now.
Where do you struggle most? Often it’s mixing up ihn (accusative) & ihm (dative), mich (accusative) & mir (dative), etc. because the English “objective pronouns” split up in two when it comes to German:
Okay, I can offer two ways that might help to get you out of your “Pronomen” pickle:
The windy road
Let’s have a look at an example:
- Simon gives Laura the coffee.
- Simon (Subjekt) gibt Laura (indirektes Objekt) den Kaffee (direktes Objekt).
- Er (Nominativ) gibt ihr (Dativ) den Kaffee (Akkusativ).
- Er (Nominativ) gibt ihn (Akkusativ) ihr (Dativ).
At first, you have to know the charts, or at least have one within reach. 
Then you need to know 3 things to replace the nouns with the correct pronouns:
- The case of the object you want to replace with a pronoun. (Dativ or Akkusativ?)
- The person of the object (1st, 2nd, or 3rd?)
- The grammatical gender of the noun, if it is an object.
Well, that’s handy when you have to create your own sentence when practicing the whole thing but what’s an easy way to identify the pronouns in a written sentence or, like in your last example, answer a question where you have to match the pronoun to an object in the question?
The short cut
The answer is declension! 
Let’s have a look at the first question in the quiz:
Erzählte Sokrates seinen Schülern die Theorie der Ideenlehre?
Did Socrates tell his students the theory of forms?
Now you could jump through all the hoops to get the right pronoun: which case is it? / is it singular or plural?? / what’s the gender??? And sometimes, if things are not that clear to you, you might have to take the long road and just go the extra mile…
…or you just take the shortcut! 
There’s an n at the end of the possessive pronoun einen which is also present at the end of the word Schülern. This means you can use ihnen as a pronoun!
If it was just one student it would be seinem Schüler. Then you know the m has to go to the end of the pronoun: ihm
If it was a single female student, it’s seiner Schülerin. So what’s the pronoun here? That’s right: ihr!
I hope I didn’t add to any confusion! It’s complex stuff with all the charts, rules, and exceptions. I guess it boils down to repetition. The more you hear them and then use them yourself, the easier it gets! If you have further question, shoot! 
My tutor deserves a giant high 5 because she did a brilliant job at helping me through this! 
