Your DataWeave survival set

Memorize these:

payload.foo
vars.foo
attributes.foo

payload map (item) -> {
    id: item.id
}

payload filter (item) ->
    item.active

payload.value default "something"

payload.amount as Number

if (condition)
    value1
else
    value2

(Field: value)
    if (value != null)

firstName ++ " " ++ lastName

%dw 2.0
output application/json
---
...

and for Salesforce:

%dw 2.0
output application/java
---
payload.customers map (customer) -> {
    External_Id__c: customer.id,
    Name: customer.name
}

If those become automatic, you're in good shape.

---

Interview talking point

If they ask:

“How comfortable are you with DataWeave?”

Don't oversell it as years of development experience. A credible answer based on your situation is:

“My previous exposure was primarily from the testing side of MuleSoft-to-Salesforce integrations, so recently I've been going deeper into implementation. I understand DataWeave as the transformation layer: mapping external contracts to Salesforce objects, working with arrays using map and filter, handling optional fields and defaults, converting types and dates, and keeping transformations separate from orchestration and validation. For more specialized functions I'd use the DataWeave reference rather than trying to memorize the entire language.”

That both acknowledges the gap and demonstrates that you understand the subject.