In a CV, where to display conference articles that became journal articles
Tl;dr: Put (published) conferences papers that are subsequently published as journal articles in both sections of your CV.
A journal article is a publication, as is a conference paper, regardless of whether the article was derived from the paper. Each publication is a contribution to science, so list both on your CV, they're both accomplishments. You can sort manuscripts by prestige of publication type, e.g., book, book chapter, journal article, conference paper, unpublished peer-reviewed manuscript, other works, work in progress, etc., optionally omitting some categories and providing incomplete listings for others (e.g., you might want to list only key works in progress). You can also cross-reference to avoid artificially inflating your accomplishments. For instance,

Journal articles
[1] anderstood (2020) A, Journal, 1(2), pp1-10.
[2] anderstood (2019) B with C, Journal, 5(7), pp59-76. Preliminary results appeared in [3].
Conference papers
[3] anderstood (2018) B, Conference, Published, pp20-27.

Note: I presume that journal articles derived from conference papers must add new material. This mightn't be the case for unpublished conference papers. In such cases, you could list both manuscripts and cross-reference, but it depends whether the unpublished work carries prestige, i.e., whether it is considered a (sufficiently large) accomplishment, which is field dependent.