"The boss needs a desk in his office."

the verb need "necesitar" i need "yo necesito" you "tu necesitas" he/she "él/ella necesita" they "ellos necesitan" we " nosotros necesitamos" to be honest it depends on the verb and the person for example the verb eat "comer" i "yo como" you " tu comes" he/she "el/ella come" they "ellos comen" we "nosotros comemos" you can see some diferences but it really helps to know the verb in infinitive

Verbs don't have a gender. You're probably confused because the verb necesitar, to need, is an -ar verb, so second person singular (which means he needs -- and also she or it needs) is "necesita" just like Daniela says.

Because it reads ".. his office" the masculine el jefe

Same!