1)
No encuentro (those) guantes que compré translates to "I cannot find those gloves I bought". You must know the gender of the noun (guantes) to correctly answer this question. Guantes is masculine; let's look at the options.
· esa - "that" (feminine)
· esos - "those" (masculine)
· estos - "these" (masculine)
· este - "this" (masculine)
The first options is feminine; it's out. Out of the last three, esos ("those") is the only one that makes sense.
No encuentro esos guantes que compré.
2)
¿Cual libro te gusto más, (this one) o (that one)? means "Which book did you like more, this one or that one?" The options are:
· ése/este - "that one/this one"
· este/ese - "this one/that one"
The second option makes the most sense here ("...this one or that one?").
¿Cual libro te gusto más, este o ese?