trener

/trener/

Cases

SingularPluralWhen to use it
nominativetrenerthe coachtrenerlethe coachesthe plain dictionary form — the doer of the sentence
genitivetrenernithe coach'strenerlenithe coaches'the owner — whose it is
accusativetrenernithe coach (as the object)trenerlenithe coaches (as the object)a specific, known object — whom or what
dativetrenergeto the coachtrenerlegeto the coachesdirection or recipient — to where, to whom
locativetrenerdeat / in the coachtrenerledeat / in the coacheswhere it is; also having — mende bar, "I have it"
ablativetrenerdenfrom the coachtrenerledenfrom the coacheswhere 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
mytrenerimmy coachtrenerlerimmy coaches
yourtreneringyour coachtrenerleringyour coaches
his / hertrenerihis / her coachtrenerlerihis / her coaches
ourtreneribizour coachtrenerleribizour coaches
you all'strenerigizyou all's coachtrenerlerigizyou all's coaches
theirtrenerleritheir coachtrenerleritheir coaches

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