Learn French: J'ai lu le catalogue et la brochure. - I read the catalog and the brochure.

It comes from lire (to read). It has an irregular past participle, lu. To form the past tense (passé composé), you use the helping verb avoir (j'ai) plus this past participle.

Is there a trick to remembering the gender of catalogue and brochure?

Words ending in -e are often feminine, which makes le catalogue a common exception to memorize. La brochure follows the standard pattern and is feminine. Knowing their genders is crucial when you want to refer back to them using pronouns!

If someone mentioned these items and I wanted to ask 'Which one?', how do I choose between lequel and laquelle?

You choose based on the gender of the noun you are replacing. If you are asking 'Which one?' specifically about the masculine catalogue, you ask Lequel ?. If you are asking about the feminine brochure, you ask Laquelle ?.

How would I ask 'Which ones did you prefer?' referring to both items in this sentence?

Because you are referring to a mixed group (one masculine item, one feminine item), the masculine plural takes over as the grammatical default. You would use lesquels and ask, Lesquels as-tu préférés ?.