Just looking at this, there seems to be very little you've actually done. I don't program that much, if any, and I probably could have framed out what you've got there, no offense.
What part are you stuck on? I wouldn't write any code for you, but wouldn't you first want to start by looking for a formula to convert grams to ounces, or something similar, and integrating that into your calculate function? The functions for input and output should be fairly basic, too-- your textbook should clearly outline how to deal with user input and output, as that's something EVERY program should do.
I mean, if you know 1 kilo is = 1000 grams, 1 lb is 16 oz, and 1 kilo is = 2.20046 lbs, you can figure it all out:
1 kilo = 35.20736 ounces
so
1 gram = 0.03520736 ounces
There you go right there. Just being me, and I'm sure someone will come with a better way if I'm wrong, I'd get the input in kilos and grams. Then, convert the kilos to grams. Convert the total grams to ounces, and then work out how many pounds and ounces are in that amount(use a modulus for that? I dunno...)
Disclaimer: I'm not a programmer, but that's what I'd think to do logically. Take someone else's advice before mine, or use my advice only in the event of a lack of more suitable advice.