Aunque la receta parece fácil, mi hermana sigue preguntando cuánta sal necesita.

Aunque means although or even though.

Here, parece is in the indicative because the speaker is presenting the idea as a real, accepted fact: the recipe seems easy.

A useful contrast is:

Aunque la receta parece fácil...
= although the recipe seems easy

Aunque la receta parezca fácil...
= even if the recipe seems easy / although it may seem easy

The subjunctive version sounds less factual or more hypothetical.

Parece fácil means seems easy or looks easy, so it leaves room for doubt. Maybe the recipe looks simple, but in practice it is not.

If you said la receta es fácil, that would be a more direct statement: the recipe is easy.

So parece fácil adds a small nuance of appearance rather than certainty.

This is the structure seguir + gerundio, which means to keep doing or to continue doing something.

So:

sigue = he/she keeps, continues
preguntando = asking

Together, sigue preguntando means keeps asking.

This is a very common Spanish pattern:

sigue hablando = keeps talking
sigo estudiando = I keep studying
seguimos esperando = we keep waiting

Preguntando is the gerund of preguntar. In this sentence, it is used with seguir to form the idea of an ongoing repeated action.

So:

preguntar = to ask
preguntando = asking

In English, this often matches the -ing form after verbs like keep or continue:

She keeps asking
= Sigue preguntando

Because cuánta is an interrogative word here. In Spanish, question words keep their written accent even inside an indirect question.

So just like:

qué = what
cuándo = when
cómo = how
cuánto / cuánta = how much

In this sentence, cuánta sal necesita is an indirect question after preguntando:

She keeps asking how much salt she/it needs

That is why it is cuánta, not cuanta.

Because cuánto changes to match the gender and number of the noun that follows.

sal is a feminine noun, so the correct form is cuánta.

Examples:

cuánto dinero = how much money
cuánta agua = how much water
cuánta sal = how much salt
cuántos huevos = how many eggs

Even though salt is uncountable in English, Spanish still makes cuánto agree with the noun’s gender.

Because Spanish often leaves out the article with uncountable nouns when talking about an amount in a general way.

So:

cuánta sal = how much salt

This works like English, where you also say how much salt, not how much the salt.

If you said la sal, that would usually refer to salt in general as a substance, or to a specific salt already identified in context.

Because cuánta sal necesita is already a complete indirect question.

After verbs like preguntar, Spanish often introduces the thing being asked with a question word:

preguntar qué... = ask what...
preguntar cuándo... = ask when...
preguntar cuánto... = ask how much...
preguntar si... = ask whether/if...

So here:

preguntando cuánta sal necesita
= asking how much salt is needed / how much salt she needs

You do not add que there.

That is the normal order for an indirect question in Spanish.

The question word comes first:

cuánta sal

Then the rest of the clause:

necesita

Spanish does not use an extra auxiliary like does in questions, so it stays more direct than English.

Compare:

¿Cuánta sal necesita?
= How much salt does she/it need?

Mi hermana pregunta cuánta sal necesita.
= My sister asks how much salt she/it needs.

The embedded question keeps basically the same structure.

Spanish often leaves subject pronouns out when the verb ending already shows the person and number.

necesita can mean:

he needs
she needs
it needs
you need, formal singular

So the exact subject comes from context or from the meaning already provided to the learner.

If Spanish wants to make it explicit, it could say:

cuánta sal necesita ella = how much salt she needs
cuánta sal necesita la receta = how much salt the recipe needs

But very often Spanish simply leaves the subject unstated.

Yes, it is normal and recommended here.

When a subordinate clause introduced by aunque comes first, Spanish usually separates it from the main clause with a comma:

Aunque la receta parece fácil, mi hermana sigue preguntando...

If the main clause came first, the comma is often omitted:

Mi hermana sigue preguntando cuánta sal necesita aunque la receta parece fácil.

So the comma helps mark the boundary between the two parts of the sentence.