Brahms Requiem? Oh, lucky -- I adore it, brava!
BY no means a dumb question! I feel this pain, believe me...! Two ways to do it. I literally just had to teach this, and to do it myself when I had to re-learn bass-clef.
Read bass clef one line or one space higher than the written note. Bass clef C (second space from bottom) is actually A (read up a space as if it were in treble clef). Bass clef D (on the 4 line from the bottom) is F (read up a line in treble clef.) So just mentally adjust up a space or line.
It takes a bit of doing to get used to, and in a pinch, just write in the notes!
Another way (I find more difficult in the moment, but this blew the mind of a kid I was teaching who only knew bass clef!) is to draw a G-clef staff, and write middle C on it (you know, one ledger line below the staff). Now draw another staff just below, this one's bass clef. That C you wrote before is C on bass clef as well. So the two clefs "connect" so to speak. So for example, the bass clef note that's 3 leger lines above the staff is G on treble clef. Count and you'll see. This way's more esoteric I guess, but more "logical" too.
2015 Connor spruce/Indian rosewood
1978 Ramirez 1a cedar