FAQ:What do I need to do when I use a CC-BY asset?
MakeHuman as such has a CC0 exception for exported models. However, that only applies for content that was provided by MakeHuman as such. Specifically it does not apply to assets you downloaded separately from the user contributed asset respositories.
In those repositories, you will find assets that come licensed in two forms: CC0 and CC-BY.
If an asset is licensed CC0, you can use it in the same way as you use all other MakeHuman assets: you don't need to do anything in particular at all when using the asset.
If an asset is licensed CC-BY however, you must live up to the obligations of that license. You are granted usage of the asset only under the premise that you tell end users of your work that you used the model in question, and who you got the model from.
It is also etiquette, but not legally required, to say where you got the model from.
Examples of how to live up to the CC-BY license
Let's use one of PunkDuck's assets as an example: http://www.makehumancommunity.org/clothes/godkiller_sword_wonder_woman.html
When producing a video, it is etiquette to include info about the asset inside the video, for example in rolling credits at the end. If this is not possible to do, then as a last resort it is acceptable to include the information in the video description where you posted the video (for example in youtube's "description" field). An example formulation would be:
This video uses the "God-killer Sword (Wonder Woman)" asset by PunkDuck'
In applications and games, you will most likely have an "about" or "legal info" menu entry or popup box. This is an appropriate place for information about the usage of CC-BY assets.
As a last resort, it would be acceptable to include information about the used assets in a bundled README.txt file. But then only if users are likely to find and read that file.