Final answer:
The appropriate word to fill in the blank is 'conozco'. The verb 'conocer' means 'to know' or 'to be familiar with'. The first person singular form of the verb, 'conozco', is used since the subject 'yo' (I) is performing the action of knowing Javier.
Step-by-step explanation:
Claro que yo conozco a Javier. Él es mi hermano.
In this sentence, the appropriate word to fill in the blank is conozco. The verb 'conocer' means 'to know' or 'to be familiar with'. Since the subject 'yo' (I) is performing the action of knowing Javier, we use the first person singular form of the verb, which is 'conozco'.
For example, you could also say 'Tú conoces a Javier'. Both 'conoces' and 'conozco' are valid conjugations of the verb 'conocer', but they correspond to different subjects.
Learn more about Using the verb 'conocer' to express familiarity