I am attempting to quilt my lap quilt using an embroidery machine and will hoop it block by block, but I am not sure if I use quilting thread on top and in the bobbin or embroidery thread and bobbin thread in the bobbin???? I have been practicing and have been using quilting thread on top and in the bobbin and it looks fine, but I didn't want to ruin my quilt by using the wrong thread.

It is your choice :D what ever pleases your eye.
The only thing you cannot use in your machine is handquilting thread. The wax in it would wreak havoc with your machine :D:D:D

i would use both the same whatever you decide to use

I use the same cotton quilting thread in top and bottom when doing quilting via embroidery machine.

If your machine is ok w/ using different weights in the top & bobbin, then do what you like. Just be sure your needle accomodates the larger weight thread on top. ALWAYS run a test swatch, with all the fabric weight, batting exactly like your quilt is, then you'll know that things will be alright; that's a good practice for any embroidery machine. If the design is moderately or densely stitched in places, you may not want to use a heavier thread, so check the recommendations of the designer, but again, test first.

Both of my machines have a special bobbin that I bought for them so I could do bobbin work. I have quilted blocks with embroidery and used yarn or floss in the bobbins. (It's thin yarn) You have to hand wind the bobbins , but it is a nice effect. I have taken classes with Betty Cotton and that is where I learned to do this.

Thanks to all for your good advice. I feel more comfortable now going ahead with this project.

Be sure and post a picture when you are done with your project so we can ooh and awww over it.

if it works and looks ok to you then it is OK

This is something that I would love to learn how to do. That sounds like it would really be a nice effect. I am working at embroidering my quilt and it looks nice. I still have a ways to go before it is finished. I will post it when it is done. Thanks for the info.