If THRIVE is coded as UISJWF, how is UISJWF coded?

Correct — A.
Rule: every letter moves one place forward (+1).

THRIVE → UISJWF:
T → U, H → I, R → S, I → J, V → W, E → F.

Code UISJWF the same way:
U → V, I → J, S → T, J → K, W → X, F → G
= VJTKXG → option (a).

Why the others are wrong

• (b)
  VJTLXG — The fourth letter is wrong: J + 1 = K, not L. Every other letter matches the +1 shift.
• (c)
  VKTKXG — The second letter is wrong: I + 1 = J, not K. A +2 step there breaks the one-place rule.
• (d)
  VJTKXH — The last letter is wrong: F + 1 = G, not H. The code moves every letter by exactly one place.

A code of a code applies the same rule twice. Find the rule from the given pair, then run it on the code word as if it were a new word.

With a +1 rule, coding twice is simply +2 from the original: THRIVE + 2 = VJTKXG, which checks the answer.

Key facts

• THRIVE → UISJWF is a +1 shift on every letter.
• Applying a +1 code twice equals a +2 shift on the original word.
• In a forward shift the alphabet wraps round: Z + 1 = A.

Common traps

• Shifting one letter by 2 by mistake: options (b), (c) and (d) each do exactly that at a single place.
• Coding THRIVE again instead of UISJWF, which only reproduces UISJWF.

No directly related past PYQ was found.