Best bet: Closer nebula with a strong power source such as a black hole x-ray stream or a near quasar.
Assuming an earth like earth, it will take a nebula with an apparent magnitude of -4 or larger to be seen with the naked human eye in the daytime. For comparison, our sun has a magnitude of -26 compared to Venus at -4. SN 1054 had a magnitude of -6!
The farther away the nebula, the more energetic the power source to make it glow and the larger the nebula. For distant nebula (hundreds or thousands of light years), supernovas are plenty energetic enough to provide illumination though they only shine for a few brief weeks or months (SN 1054 shown for two years). Perhaps a nearer nebula (at tens of light years range) illuminated by the x-ray jet of a nearby black hole or a stellar nursery of supergiant stars would do the trick.
For comparison, the Moon is about 1/2 a degree wide and we can see it quite well. Using an apparent size calculator we can get an idea of how large something will appear from a given distance. Since the units don't matter, only the ratios, we can plug in a size of 10 (light years) and a distance of 100 (light years) and get an apparent size of 5.7248 Degrees or about 11 times the width of the moon.
A similar concept to your nebula is the Eye of Terror in the Warhammer 40K universe. The Eye of Terror is some 20,000 light year across.