The Benedict's test uses Benedict's reagent, which turns from a transparent blue color to an opaque yellow, orange or red color in the presence of reducing sugars. Reducing sugars include all monosaccharides and many disaccharides. Monosaccharides are the most simple sugars such as glucose and fructose. Disaccharides include two monosaccharides bonded together and include lactose and maltose.
To use a Benedict's test, you dissolve the food sample in water and then add about 2 mL of Benedict's reagent. You then place the sample into a hot (even boiling) water bath. Stay with the sample so that you can monitor the color change and remove your sample when it is completed. If there are monosaccharides or disaccharides present, the solution will turn color within 2-4 minutes. If your water is not boiling, it may take a bit longer.
The Benedict's test is much more qualitative than quantitative, but the more red the solution turns, the higher the concentration of simple sugars present. This is shown on the image below.
Your question involved specific foods such as fruit, jam, bread, pasta and coffee. Fruit contains high amounts of the monosaccharide fructose, so it will result in a positive Benedict's test. Jam contains fruit that will have fructose in it, but it also contains large amounts of added table sugar, sucrose, which is a disaccharide that happens to not result in a positive Benedict's test. Jam will result in a positive Benedict's test, but only because of the sugars present in the fruit, not the added sucrose. Bread will often times produce a positive Benedict's test, but the results vary depending on if the bread is white bread or whole wheat and any additional ingredients. Most carbohydrates in bread are in the form of starch, which does not produce a positive Benedict's test, but some of that starch may be broken down during the hot water bath which can then produce a positive test. The same is true for pasta as it is for bread. Coffee by itself does not contain any sugar and so will result in a negative Benedict's test.
So, if someone eats mainly fruit, jam, bread, pasta and coffee, they will likely have fairly high blood sugar, which could theoretically be seen in a Benedict's test, because of the monosaccharide sugars in fruit and jam, and the starches in bread and pasta that are broken down into monosaccharides in the body. The coffee would not contribute to the blood sugar levels.