Learn Spanish (Latin America): No podemos encontrar nuestras maletas azules.

You are right that poder (to be able to) is an 'o to ue' stem-changing verb. However, the nosotros (we) form is an exception to this rule in the present tense. It keeps the original 'o' from the infinitive, making it podemos. The other forms do change (for example, yo puedo and tú puedes).

Why is encontrar left in its infinitive form instead of being conjugated?

When you have two verbs right next to each other where the first one acts on the second, like 'can find' (podemos encontrar), you only conjugate the first verb. The second verb stays in its infinitive (the dictionary form ending in -ar, -er, or -ir). By the way, encontrar is also an 'o to ue' stem-changing verb, but since it is not conjugated here, its stem does not change!

Why is it nuestras instead of nuestro or nuestros?

Possessive words like 'our' have to match the noun they describe in both gender and number. Since maletas (suitcases) is feminine and plural, you must use the feminine plural form nuestras.

Why is the word for blue spelled azules here?