en_tn_condensed/jhn/08/18.md

I am he who testifies about myself

"I give evidence to you about myself"

the Father who sent me testifies about me

"my Father who sent me also brings evidence about me. So you should believe that what we tell you is true"

the Father

This is an important title for God. If your language must state whose Father this is, you could say "my Father" since Jesus switches to that in the following verses.