sonet

/sonet/

Cases

SingularPluralWhen to use it
nominativesonetthe sonnetsonetlethe sonnetsthe plain dictionary form — the doer of the sentence
genitivesonetnithe sonnet'ssonetlenithe sonnets'the owner — whose it is
accusativesonetnithe sonnet (as the object)sonetlenithe sonnets (as the object)a specific, known object — whom or what
dativesonetgeto the sonnetsonetlegeto the sonnetsdirection or recipient — to where, to whom
locativesonetdeat / in the sonnetsonetledeat / in the sonnetswhere it is; also having — mende bar, "I have it"
ablativesonetdenfrom the sonnetsonetledenfrom the sonnetswhere it comes from; also "than" when comparing
When to use each case
nominative
the plain dictionary form — the doer of the sentence
genitive
the owner — whose it is
accusative
a specific, known object — whom or what
dative
direction or recipient — to where, to whom
locative
where it is; also having — mende bar, "I have it"
ablative
where it comes from; also "than" when comparing

The endings are the same ones the pronouns wear — that page explains when each case is used.

With an owner

One ownedSeveral owned
mysonetimmy sonnetsonetlerimmy sonnets
yoursonetingyour sonnetsonetleringyour sonnets
his / hersonetihis / her sonnetsonetlerihis / her sonnets
oursonetibizour sonnetsonetleribizour sonnets
you all'ssonetigizyou all's sonnetsonetlerigizyou all's sonnets
theirsonetleritheir sonnetsonetleritheir sonnets

The overlap in the last rows is real, not a mistake: sonetleri can mean "his / her sonnets", "their sonnet", or "their sonnets" — context decides.